Recumbent vs Upright
I ride a short wheel base underseat steering recumbent bike (Roadboy) for my road tours and a 29er full-suspension mountain bike (Proud Mary) for my back country tours. I much prefer the recumbent bike and would have used one for my back country tour of the continental divide if it had been practical. The comfort of a recumbent bike, for me, more than compensates for it's minor disadvantages. The disadvantages of the recumbent bike must seem obvious to the casual viewer, as evidenced by the three standard questions I've gotten wherever I tour.
First, people want to know how it climbs. Most people assume that a recumbent bike cannot climb as well as an upright bike. Once in France I was asked from where I had come and I replied that I had come from Spain over the Pyrenees. This disbeliever pronounced me a liar, evidently considering it impossible that I could have climbed the Pyrenees on my recumbent bike. I had not cycled much when I started touring in 1999 and I started with a recumbent bike, so until I had spent some time riding Mary I couldn't see how a recumbent bike would have a disadvantage at climbing. The common assertion that an upright bike must climb better than a recumbent bike because you could use gravity to help you push on the pedals seemed obviously wrong, from simple physics. But, some time with Mary convinced me that I could climb better with an upright bike than a recumbent bike. I think a couple factors explain this characteristic. First, when climbing a cyclist tends to bend at the waist, this reduces the angle between the torso and the upper leg, evidently providing more power to the pedal. A recumbent rider cannot bend at the waist, the angle between the upper leg and the torso depends on the angle of the seat. Second, standing up to pedal, while very inefficient relative to sitting, does bring different muscles into the activity. The shoulder and arm muscles can contribute to the effort, giving the leg muscles a little rest. However, I think the upright bike has only a small advantage relative to the recumbent bike at climbing hills. I've cycled with some people close to my age and fitness who climbed more slowly on their upright bike than me on my recumbent bike, others on recumbent bikes were faster than me on an upright bike. I think the strength and fitness of the driver dominates this comparison, but the upright bike seems to have a small advantage.
Second, people want to know how I start. Once in Belgium, surrounded by a bus load of tourists from India, I used their curiosity about how I started to persuade them to clear a path so I could get on my way. Starting isn't hard but it's more difficult than with an upright bike, especially if pointed up hill. I set my brakes, put one foot on a pedal, then push off with that leg while bringing up the other leg in time for a second stroke. With cleated shoes and pedals it's a little tricky but works quite well with a little practice. The slight extra difficulty of starting with a recumbent bike shows itself most severely in stop and go city traffic. The recumbent really likes to cruise the open road rather than stop and go at signal lights and stop signs. Fortunately, I like to tour in the country rather than the city so I get along just fine with Roadboy's preference for the country lane.
Third, people want to know if it's stable. Of course, the gyroscopic effect of rotating wheels, the phenomenon that makes cycling possible, works just as well for a recumbent bike as an upright bike. So, in principle the upright bike should have no advantage here. But, I must admit that the position on the bike just doesn't seem natural. Additionally, the geometry of a short wheel base bike like mine generates instability. For example, I could never, even for a very short distance, pedal my bike with both hands off the handle bar; I would certainly crash. I've heard of other recumbent drivers, evidently more skillful than I, who can pedal with out holding on to the handle bar but I have not seen this feat yet. It gets worse, if I start to fall then I have to lower my foot down to the ground, instead of just putting my foot down on the ground like an upright driver. Once my stabilizing foot gets to the ground I'm not in a strong position, with my leg bent at a right angle. Once starting down I'm likely to continue until Mother Earth catches me, not too gently I might add. An upright driver simply needs to stand up, already in a natural standing position for which humans are well adapted. On the other hand, with some experience I've been confident enough of my balance to negotiate mountain trails in Switzerland, and pedal trough urban obstacle courses composed of pedestrians, automobiles, and various road hazards. Of course I've fallen, fallen many times. But, I don't have far to fall and I never go over the handle bar head first. When I fall I almost always bounce along the road on my butt, with my feet out front too protect me. I've never suffered serious injury.
The recumbent bike has other more subtle disadvantages. As mentioned, I must always keep one hand on the handlebar, so opening a candy bar on the move can provide a nice adrenalin hit. I'm lower and more vulnerable to dogs. If a dog bites my foot or hand then I'm likely to fall, probably stimulating the final step in a dog's inherited hunting program. Recumbent bikes are a little heavier and more expensive. I have two different wheel/tire sizes so I have to carry two extra tubes and tires, instead of just one. Recumbent drivers can't turn around on their bikes and look backwards very easily, at all. (Get and use a rear view mirror, preferably a helmet mirror.)
On the plus side, Roadboy provides endless opportunities to meet people. I've had people stop driving to take my picture, cheer as I passed by; bus loads of tourists slow down to my speed, cameras clicking in a frantic clatter. Imagine a small iconic Spanish town with a central plaza, water fountain in the center, small restaurants around the periphery. On a busy day the scene can go quiet when I pull into the area, the kids stop playing soccer, the parents stop eating, all stare at the odd contraption coming into town. Perhaps only in Germany and Belgium did Roadboy fail to capture the attention of all who could see the strange device. Children especially find Roadboy just fascinating. One little boy was yelling at the top of his lungs to his mother, "look at the funny bike". As I passed I heard the patient mother explaining to her son that my bike was probably broken!
In the end however, the comfort of the bicycle dominates all else. At the end of a long day I'm tired, but not in pain. My favorite picture of me on my bike was snapped outside a grocery store on the Pacific coast. I was riding with some German friends who had gone into the store to buy the nights dinner while I guarded the bikes outside. I leaned up against a post to enjoy the warm sun and that soft inner peace of a tired but not exhausted body after a long day. They came out and snapped a picture of me sound asleep on my bike. Find me another bike that doubles as a Lazyboy recliner and I'll buy it instead. Don't tell Roadboy of my fickle devotion.
Recumbent vs Recumbent
Recumbent bikes come in one four configurations defined by two binary options. Recumbent bikes can have the front wheel behind the pedals or in front of the pedals, known as short wheel base (SWB) and long wheel base (LWB). Additionally, the design can either position the handle bar for above the seat steering (ASS) or under the seat steering (USS). You can see that Roadboy has a SWB and USS. I have another recumbent bike configured as SWB and ASS. I much prefer USS to ASS. With USS my arms hang loosely and comfortably at my side. I must admit that it takes little effort to grip the handle bar of an ASS bike, but why subject myself to even that little effort. Well, it turns out there are a couple reasons. Wind tunnel tests have shown that ASS bikes slip through the air more efficiently than USS bikes. Also, ASS bikes are probably more popular because they seem more accessible to a new rider. Nevertheless, I like my underseat steering, if for no other reason than the attention it gathers. A bike with USS looks all the more odd. I've even had people miss my handle bar altogether and guess that I steered the bike by leaning one direction or the other. Having not read my web site they did not know that I can't take both hands off my handle bar even for a moment.
As for LWB vs SWB I can't say anything from personal experience; I've never even ridden a LWB bike. I purchased a SWB bike to help me with shipping and to facilitate transportation on trains in Europe. I've often thanked myself for that early decision. Since the purchase I've read that SWB bikes may climb a little easier than LWB bikes. Specifically, at slow speeds it's easier to maintain your balance with a SWB bike than a LWB bike. That works out very well for me, for the obvious reason. However, I've read that LWB bikes track the road better and don't require such careful attention. People seem to like best the choice they made for whatever reason.
Bicycle Setup
I suppose I should point out some obvious tips about setting up a recumbent bike for touring. Of course, you'll need a rear rack. If you get a PanPack then you'll need to make sure the width of the rack fits the width of the middle compartment on the PanPack. I also managed to attach some low rider front racks to the frame of my bike, just below the seat. Many recumbent manufacturers make available custom fitted small racks for under the seat panniers. These panniers not only carry more stuff (maybe more than you should) but provide very convenient storage, under the seat bags function like handle bar bags for upright bicyclists. I keep snack, camera, sunscreen, rain gear, etc. in my underseat bag. One tip, be careful about the clearance above the ground. If the bag hangs too low then it will rub the ground on short turns.
Most every recumbent driver I've seen has found a way to attach a water bag to the back of the seat. My water tube hangs down at my side where I can easily find it and get a drink whenever I want. It's so much easier than using a water bottle. Even better, it can function as a dog deterrent. I got this tip from a recumbent driver on my Pacific Coast trip. Pursued by a dog, he let some water trickle out of his bag onto the ground, the dogs immediately stopped to smell the water, I think they can't resist the temptation.
I started with a handle bar mirror, then switched to a helmet mirror. It took me some time to learn to use the helmet mirror but now I can't imagine riding without it.
I prefer Presta valve tubes over Schraeder valves, but you can't always get what you want. Many recumbent bikes use 26" mountain bike wheels for the rear and Presta tubes for this size can be hard to find at WalMart, or, just choosing randomly, a local hardware/general store in some small town in Greece. Get your bike shop to drill a larger valve hole in your wheel, then use a small adapter for the Presta valve. If you need to use a tube with a Schraeder valve then you only need to remove the adapter. It may save you a long walk in, well, Greece.
Mountain Bike Touring
I have very little to offer regarding touring with mountain bikes. I took two summers to complete the Great Divide route. I can tell you that the standard rig for that trip has settled on a BOB trailer and two small front panniers to hold the front down. This setup seems the most stable and is the most popular rig on the trail, although I've seen most everything else, including a folding bike.
My mountain bike, Proud Mary, is a so called 29er. That is, it uses 700c wheels in contrast to the more common 26" wheel. ("Proud Mary keeps on rolling ...", Credence Clearwater Revival, get it?). The bigger tire and larger ground patch supposedly provide the bike a little more traction and more efficiency rolling over rocks. I can't say that works but over a summer I did determine that the bike was noticeably more efficient in sandy conditions. I rode the first summer of the Great Divide route with a large group of people. In a large group you find people who ride just a little slower or just a little faster ( or in my case just a lot faster ) than oneself. I found that in sandy conditions I was able to keep up with people who were normally rather faster than myself.
Mary has full suspension. You'll certainly want front suspension, and most of the riders I saw on the route had full suspension. I think it's worth the extra weight to arrive in camp a little less shaken than stirred. Your mileage may vary.