So... let's talk megas.
No actually, just two.

When I am bored about all these cookie cutter ou teams, i sometimes play the other tiers.

The only megas I have touched so far are Charizard X and Y, which are awesome, Mawile, also awesome, and Blastoise, Medicham and Gardevoir, which aren't that impressive it seems.

Now ubers, that's completely new terrain for me.
I would love to run my old pal Mewtwo with its mega.

How good or bad are they?
I heard Y is absurdly high on the sp. Atk and therefore hits like a plow