SandyBoi said on, Mon Mar 07, 2016 10:57 am.
I did say that my favourite is Mega Gardevoir earlier, but I've got another pokemon that's also been a great one for me.
The ability Scrappy (which it has before Mega evolving) helps it attack Ghost type pokemon, as this ability allows any normal and fighting type moves to hit ghost pokemon.
Then when it does Mega Evolve, it has the ability Parental bond, which "Allows the Pokemon to hit twice with the same move in one turn. Second hit has 0.5x base power. Does not affect Status, multihit, self-KO, or spread moves (in doubles)." (Taken from Smogon)
I've got a Jolly one in ORAS, with the moves Fake Out, Power-up Punch (Raises attack by one stage with each hit), Crunch (Though I'm not really sure whether to replace it with Sucker Punch, given the downside of using Sucker Punch) and Return.