Second topic of this nature in one evening, I'll try to be a bit more elegant and careful in what I say this time.

Whenever deciding on any forum software try them all out to give careful consideration
Don't rely solely on the information given on the official websites/forums (Possibility of bias/selective editing)
Do some thorough research (google is your friend)
Consider important factors, not just features
- Trust/Reputation (Good/bad/newcomer)
- Security (find expert reviews, discussion of prevalency of exploits, which do 'experts' recommend)
- Features (+ expansion of features via plugins/mods/hacks)
Always make an INformed decision
Also remember the permanency of your decision. Usually there are conversion scripts, is there one available to another software, is one going to be available soon?
My own opinion/recommendation for whats its worth having used a variety and not out of loyalty to any particular forum software.
[free] SMF
[paid] Vbulletin