Best forum software

[Tomisimo]

Right now this forum is running on SMF forums software which is a free product. I've been having a few issues with it, and I'm considering changing over to some other forum software. I'd like your input if you have an opinion. I'd like to get moved over to a more permanent solution before this forum gets more popular, because I have a feeling it's not going to be that easy to import all the users/posts etc that there are right now into a new software product.

Here are the programs I'm considering ATM.

PhpBB2 - Free, with some security issues
VBulletin - Not free (actually quite expensive $160), but with a great track record for security and great features. This already has an import utility to import from SMF.
Lussimo vanilla - Free, looks good but it's a largely untested program.

If you have an opinion on which one I should go with, or if you would like to suggest a different piece of software, please do