I heard P3 paints weren't that great, actually. A lot of people give props to the Vallejo and Reaper paints, though it's true that Citadel metallics are probably the best (and the foundations/washes are great).
I love Vallejo simply because the dropper bottle design is much better than GW's paint pots, though you have to give Vallejo paints a good shaking because they separate easily. Vallejo also has close matches to the Citadel paints in their Game Color range (they have similar names, some are pretty damn obvious).