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YABB (Yet Another Bulletin Board) also free, perl based
Over these, I convince clients the $160 license and $40/annual renewal is well worth the investment for vBulletin.
See what people are using most of, this will tell you "what's best."
If you have the money I would pay for vBulletin. However, you could also start with a free program such as SimpleMachine and then update the software to vBulletin once you get traffic and think your site has potential to generate revenue.