Trigger & Defrocked Priest have called this one correctly. It's Wolves v West Brom. i seem to remember some official study/research on this subject a couple of years back, taking into account all the different variables, and the 'winner' was Wolves v West Brom. (and i have been to it with a Baggie mate - and can verify it's proper f***ing mental !)
Have you ever been to Oxford v Swindon? They HATE each other, I know a lino living in Oxford who will not even spell out the name and drives around it if he has to.
I went to a game at the old Manor Road ground in the Cup a few years back (actually 40+ - gulp) and the crowd never stopped booing and whistling if Swindon, particularly Don Rogers, had the ball.