Who makes the best seat for long distance riding?
The Ultimate seat is your friend.
I have the Ultimate 4 pc Big Boy and it's great. I think the Mustang is a good one, too. I ran a poll on the main VTXOA board and Ultimate edged out the Mustang slightly. It's really a matter of personal preference so the best thing to do is to sit on both to see which you like better. Even better if you can test drive before deciding. I've also heard the BadX seat mod is great, too, but haven't ever sat on it.
Gawd I need a new seat, my butt kills me on anything over 30 minutes.