Can't say anything about Prague but according to Dan, Prague obviously had quite a competitive air about it but he also said that there were groups (e.g the Russians stayed within themselves, as did the Italians, etc...)
Amsterdam was absolutely crazy, the favouraite days of my life that I can remember, everyone was really nice but there were some people who didn't really freestyle or do anything which was a bit sad because they'd made the trouble to go.
However, Azun and the Russian guys will be at Prague so if that's your main priority go there, but if Skora, Rocco, Azun, etc... decide to go to Amsterdam, I'd definitely go.