Skeet in the states is gun up. That's the way they are taught, end of!
However in the UK where we have seemingly more wind and rain during the competition season we have top shooters who shoot skeet using both gun up and down. There is no right or wrong way, its what works for you and in many instances its usually the way your coach shoots.
I shoot skeet gun up, because.I find it is less to think about. Having said that if I had my time over again with the experience I have I would shoot gun down.
I think it is a much more relaxed shooting style and easily transferable to game shooting / sporting etc.
For those thinking about shooting skeet to a top level, get a lesson from both Todd bender and Joe Kitson then choose for yourself!!