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BW2. No, seriously if you want a different gen other than ORAS which actually some people know how to play instead of shit like RBY, and is fun to play too, just make a BW2 tournament.
I have nothing against RBY except that only a minimal amount of players actually have a team/knows how to build a team. Perhaps if we had a project that allowed us to explore RBY further then it would receive more attention. However at this point it's basically ignored and as a result wouldn't be quite successful in Weekend Tournaments.
Well considering rby ubers was ou+mewtwo and mew, am not sure it'd be big. For GSC, ifound this: http://www.smogon.com/forums/threads/gsc-ubers.3454861/
it looks better than RBY, but still unappealing. ADV best cos different mechanics
we've had lots of bw2, and just now had iris v iconic in dpp, adv is a lot different due mechanics, items, and moves, i think it would be cool(also wth happened to teambuilding competition)