I was going to start building a special attacking team with an Azumarill, but I can't deside because both of then are really good too.
These two can Mega-Evolve and are found in the game. They're superior to Espeon or Meowstic; Alakazam is faster and hit harder while Gardevoir's Mega Evolution makes it amazing, with its already expansive movepool. Kirlia is easy to train too. Now Abra's hard to find since it always flees with Teleport, which can be very silly. So if you hate Gardevoir and won't bother seeking an Abra, um, between Espeon and Meowstic, pick Meowstic, easier to evolve and has a better movepool.