I've got an IC/Amtran 3000RE that's still in the demo process, but I wouldn't change a thing about it- except an air ride driver's seat. Its a 75 pax bus that, even though it's just me and SWMBO, has plenty of space for a decent floor plan. Personally, I like transit style buses, they feel more maneuverable than dognose buses, and the pusher engine allows me to have a conversation up front.
What to stay away from? Gassers in full size buses. You'll have to plan your trip from truck stop to truck stop and get lousy mileage as well. Rust is another big thing, and sometimes buying sight unseen on an auction site can be hit or miss. My bus has spent its entire life up north (Connecticut, Wisconsin, Newfoundland), and (so far) not a rusted out hulk.
I know the rest will chime in. Listen to their advice so that you can make an informed decision