I would rather go with SMF or MyBB. I've bought vBulletin and it's fucking crap! I switched from SMF to vBulletin but I really regret it.
The updates are often buggy sometimes they dont work at all, the support is fucking crap and you often need to search their forum forever until you find some dude that fixed the code for them.
And even when they got some code to fix the problem they dont even use it in their updates. They're fucking cunts. Dont buy vBulletin!
http://www.simplemachines.org/
http://www.mybb.com/