To me, it depends on what you plan on using the forum system for. I'd say this for the following forums:
1:vBulletin for flexibility and expandability, along with it's ability to keep extremely busy site's servers up and running
2: SMF for the cost (free!) and because it's closed source
3: phpBB if you want to risk using 100% open source software/wish to mess around, or want to use it because it's free.
4: IPB if you want a quick, professional looking forum up and running and don't plan to modify it much.
Definately IPB. It is so easy, and for some reason, I just LOVE its design. It has many cool moderation features, it is easy to mod, and actually, its similar to myBB. Lots of features of myBB are similar to IPB. So if you like myBB, try IPB. Trust me
SMF 2.0 is faster, and is at its RC stages, and RC 2 will be out soon, i predict the next one to be the final stable release.
Its administration is already improved beyond compare, the same goes for its functionality and ease of use. It has become the number 1 forums software in my books, i have already tried
- Simple Machines
and have seen many instilations of vB
Ive tried more then what you have on the list.. there was one called orca... it was all ajaxed but they intentionally have bad instillation instructions so they can convince you to pay them extra money for instillation. (thats wat i think anyways).
My list of softwares i have tested goes on and on though so cant re-call all
As far as free forum software, I really like phpBB. It seems very extensible to me. It's really easy to integrate user sessions and things such as that. The phpBB community is great. You can get any problem solved in a few hours -- very responsive community.
For paid forum software, I am absolutely in love with IP.Board. Their system is beautiful!
Just a note, this would've been great as a Poll.
But, I have my own Forum, I recently made, I like it, it's userfriendly, but also, if you are wanting to go in depth more, it's simple to do. URL: http://teen-topics.express-forum.com