Japanese. They just seem to be better made and vary a lot more than the English ones (and are longer). I'm sure the English ones use synthesisers for the background music for the songs whereas the Japanese ones obviously don't (except High Touch, I think). I mean, if you compare Together to Spurt to Ready Go, they're really different. But the English ones sound rather samy from the 4th-8th, I can't quite put my finger on it how they are, though. I also really like the Italian ones because they're really catchy, but Japanese is usually the best.
Don't the Chinease and Korean openings just translate the Japanese openings (or at least keep the same opening theme and put in whatever lyrics) rather than change it like everyone who gets the dub from 4Kids/PUSA?