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Depends, OP. Competitive or in-game?
In-game, do all. Who gives a fuck what people think about your choices.. it's not as if the main games are EVER hard. It's just more about building a team of pokemon you truly like, and if you truly like them, hell, use them.
Competitively is a little different. It's hard to say on a number of instances.
First, we don't know the metagame.
Second, we don't know for sure the inherent use of the Megas (though they're looking good).
Third, it all depends on the rest of your team, unless you intend on building the team AROUND the megas.