Edit for more information:
I'd like to know which would be better for my XY team. Originally I was planning on sticking with Gardevoir but you get the Gardevoirite after beating the Elite Four, plus she doesn't learn any fairy type moves until level 85, which is a bit late (and you get TM Dazzling Gleam later as well), so her secondary typing is a little useless offensively. I really like Malamar's ability 'Contrary' and it would have it's advantages, but he's 4x weak to bug and Gardevoir has better stats anyway. So I'm a little torn as to what I should do.
Bug is uncommon after the Bug gym, which happens pretty early. If you really needed to, you could also get something like Honedge, Charizard, or Lucario tank Bug moves. Gardevoir has low Defense and HP, as well as Delphox/Greninja/Lucario/Charizard/Squirtle/Venusaur being better for an in-game team. I think you should use Malamar and Mega Evolve Lucario or whatever Kanto starter you use instead. :P
Hope I helped!
Malamar would be your best bet here. Malamar has a better move pool and the bug type weakness isn't a bug deal. (See what I did there?)
But seriously Malamar is a bit better.