I've tried SMF, vBulletin, and pbpBB. All are fine forum software. SMF is the easiest to modify, in my opinion. The original Groovy Gamers used a phpBB 2.0 forum, but I had problems with spam. I switched over to SMF 1.0 for Groovy Gamers II. I think tried vBulletin on my own forum. I decided to go back and try pbpBB on this forum, to see if it was much improved from 2.0. I do think it's easier to admin, so far...
I'll give you more opinions as we move farther along. ;)