Clean install of 8.1. Power users and gamers love 7 because it doesn't force them to see the creature comfort active tiles in the metro desktop that requires all of one click to vanish and you're on the desktop.
Performance wise if your PC is relatively fast you're not going to have any decipherable difference between 7-8.1. Honestly why wouldn't you want to newest OS for free and be aware of the developments being made to improve and change the Windows OS environment.
Like many, I've been running 8 since the beta and its rock solid stable and I kinda like the metro screen at boot. The Metro screen looks pretty cool at boot with the active tiles spanning 3 screens in eyefinity. However, I almost never use any of the metro...