Just to throw something else out there, what about ubb.x and ubb.threads? I don't believe comparing VB to UBB is fair, I think comparing ubb.x and ubb.threads would be a better comparison. UBB is really in its own category anymore. As someone earlier in this thread stated, UBB is really meant for small to medium size sites.
I wasn't all that impressed with the look and feel of threads pre-6, but the version 6 is looking good IMO, and as IP has it longer, I'm sure the look and feel will gravitate more toward the classic UBB (just my opinion).