Most long distance tour bikes are not mountain bikes! Though I admit it does have to depend on what you're going to be riding on. If you're doing a trip on mountains, yeah...but otherwise most people will ride predominately on the paved roads, and mountain bikes are really super slow on roads, and will tire you out like nothing. Have you ever ridden a road bike up a paved hill? The road bike will lean into that hill and practically pull you up. A mountain bike on a paved hill will have you cursing while you are pumping your legs in squares, crawling up that hill. You want something that can carry a rack (carrying a backpack will wear you out), drop handle bars so that you can change arm positions, if you want knobby tires instead of slicks, so you can off road, and preferrably three chain rings, but at least two so you can get into a good granny gear for those hills. There are always a lot of hills, even when it's flat. You do not need anything expensive, but you do need to know how to change your flat on the road, and adjust your breaks, minimum. Try it with the mtn bike though, if you have nothing else. A lot of people do ride long distances with them and love them. Remember to pedal in circles, not in squares. And as far as how long you can go, that's up to you. Usually about 60 miles or more a day. Make sure your knee is in line with your heel, when you've got your leg extended on the pedal. Any angles will hurt your knees. Also make sure that when your leg is extended, it's neither over extended, nor under extended, b/c that will either strain your leg, or shorten your stroke.