vBulletin is the best of them all and it's worth it's price. IPB is not bad at all but I would recommend you vBulletin more than IPB for it has more options among other things.
If you want to avoid to buy a licence for a board, I suggest you MyBB more than phpBB or SMF because it is simply a free version of vBulletin. It doesn't have all of the options that vBulletin has but it has the main options in admin panel, mod panel as well as all the stuffs needed for posting.
