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[Black117]

To be honest, I don't have any recommendations or certain Pokemon to tell you but I think the best approach is to use the teams found on Nugget Bridge or other dedicated sites since you can see what others use. That's how I started out since I'd ditto a core I like and just teambuild from there. Of course there's going to be less "originality" but you said yourself the only thing that matters is winning games.

For individual Pokemon, Mega Kangaskhan and Mega Salamence stick out though I've seen a fair usage in Chariard Y and Mega Gardevoir lately. If you really want to win games, build around some CHALK cores honestly (Cresselia, Heatran Amoonguss/Aegislash, Landorus-T, or Kangaskhan).