Originally Posted by robow
Simple, a bike that fits you well and that you're comfortable on for long hours at a time. The rest is all fluff
To the OP ...
1) What type of bicycle(s) are you currently riding, or have you ridden in the past?
2) What do you like and dislike about them ... make a list.
3) When you ride with others, and look at their bicycles, what do you like and dislike about them ... add those features to your list. (Feel free to look through the sticky threads here of loaded touring bicycles, and websites/blogs etc. to see what other cycletourists might be riding.)
4) Browse through bicycle websites and magazines and see what's out there that might match your list. Make a list of possible bicycles (and their manufacturers). When I got to this point, my first list of possible bicycles contained 50 bicycles and just about that many manufacturers.
5) Read up in detail about the bicycles and manufacturers on your list. If you can, have a look at the possible bicycles in shops, or on group rides. Then narrow the list. At this point things like budget and shipping etc. might come into play. (For example, Seven dropped off my list at some point in here because although I really like them, they are way out of my price range). And keep narrowing until you've got what you want.
The process took me several months before I finally made my decision.
If you don't have any bicycle right now, just pick up something relatively inexpensive that seems good ... you can use it to get some riding in, and to determine your pros and cons in your decision-making process. Then either keep it as a commuter bicycle, or sell it, or give it away when you get a bicycle you really like. Or maybe you'll love it, and decide to use it for your ride!
If you need a list of manufacturers to consider, some of us might be able to help you with that.