We recommend SMF over vBulletin or phpBB
Although these are both fine forums, phpBB has a bad track record concerning exploits and over the last couple of years, has had several fixes for security reasons. Some people don't keep up to date, which puts their accounts at risk.
vBulletin tends to use slightly more resources than SMF, in our experience anyway, although it is a smart board too.
The winner in my opinion is SMF, because it's really easy to upgrade and put a new theme on it.
For the resource usage, I think it's been covered, the 2 people involved here both understand what is happening now I think. Stapel, I'm just on your ticket now, I will get back to you right away. Support is a bit busy at the moment, but we are working through the steadily. Sorry for the delay.