I like vBulletin best. UBB (which was the old software used by this board before vBulletin) is also easy to use.
I don’t like Webcrossing bulletin boards as much. The interface is very much akin to usenet newsgroups as viewed in a newsgroup reader. You only see the new posts unless you actively do something to fetch the previous chunk of the thread, so you’re perennially landing in mid-thread when you click an interesting subject.
Far worse are About.com / Delphi bulletin boards. (It looks like they are upending their whole system and starting afresh and I haven’t used the new version anywhere yet at all). As with Webcrossings, you open a thread and only see the “unread” posts and you have to click links to backtrack and get the whole thread from the outset. And you can’t view the thread while you’re posting to it unless you open a separate window for it. I hate the way the thread list is in a tiny subwindow and you’ve always got one thread open in midscreen. Navigation from one thread to another without losing your thread-list is a real bitch.
Worse yet are Yahoo bulletin boards. Worst text-wrap I’ve ever seen, and there’s no easy way to bring up a list of threads as opposed to posts, i.e., if “Hello from a Newbie” received 20 new posts you’d see it listed 20 times for each of the 20 new posts when you look for what’s new.