phpBB: phpBB was the first ever board that I ever chatted in, which lead to my first board I admin-ed [on a subdomain] and from there, the experience just grew. The hacks took me several days to complete, the instructions weren't really clear, but thats not all. For the schemes, they are not really customiable, and a lot of graphics to do with. They do not have collasable categories/forums and that proved a hindrance because of the activities in my forum. The permission settings can go konky sometimes and ordinary members could see my admin's forum from time to time.
ETA: You have to change templates in the file itself, so it doesn't really serve its purpose.
Ratings: 6 half/ten
Ikonboard: Collapsable forums were a plus, but besides that, there wasn't much to modify and the feeling just wasn't there for me.
*Shrug* I only used Ikon for 2 - 4 days, so.. Yeah.
Ratings: six/ten
Invision: I've tried both invisions [on the free server, and on my own] and the only thing I dont like was how the header couldn't be modified - There was always the image that couldn't be removed. The hacks were relatively okay, and I could get some good support, but some people were hostile and I stopped using invision after a few months.
Ratings: 8/10
vB: What I am using now. Definitely customiable, great support for both the board and hacks, and the best of the lot. Modification of the templates were easy enough, and with some help, I installed the hacks pretty easily.
Ratings: 9 half/10