Hi everyone I use currently PhpBB, but i've heard, that there are much better systems that that.

I'm looking more into ajax/javascripted/flashed sites.

Here are some more criterias:

Nice and extensive control of users, forums, topics, etc. Not neccesary the easiest, i'm not that bad at trying things.
Customization in themes, addons. Also the variaty of them. (btw, i've looked over the net for ~10 minutes, i couldn't find any premium or free themes (solid themes) for myBB. And i'm very bad with PS, i'm a coding guy more likely, but not very advanced, jsut changing things pretty much).
Ajax/javascript/flash support, i mean same thing like in IPB, those fading tables, etc. I've made a nice menu using javascript for my PHPbb board with a lot of help from their forum...
Reliability. I don't know what else i could want from those boards, everything else is just addons and plugins...

Anyway, so let's start the discussion. Why do you prefer some forum system and why?

P.S. i'm not able to buy anything for 80$/year as a student in a poor country, so i cannot afford IPB or vbulletin or anything like that. So let's stick with free CMSes.