I've been a big fan of phpBB for a long time,
never actually had any real experience with vBulletin.
Then came "THE CHANGE". Forum I was moderating got changed to vBulletin -- thanks Temi (I'm not being sarcastic!).
One of the best things that could happen. The Admin CP is way better, plug-ins are easily found, setup is way easier.
I couldn't care less about phpBB anymore.