Personally I think SMF is a great choice. phpBB updates quite alot which is good to prevent problems with hacking and such, but it is still quite prone to hackers abuse.
Free IPB is like..too exploitable.. I´ve heard actually bad things about the free one. Only use IPB if you use the good, bought software, like version 2.0 or any updated up to date version.
There is also vBulltin..quite expensive for what you get, but it´s very nice.
If you want free, use SMF, or phpBB, before you use IPB. Ipb is also complicated, and sometimes hard to administrate. phpBB is too easy. xD