Which Gallade- the Mega or the one from Breakthrough?
I'd say the best partner for Mega is Forretress (FLF), because it puts lots of damage on the board instantly, ready for Gallade to sweep across. Then Mega Turbos and Dimension Valley, with maybe Spinda or Gengar-EX as a backup.
The Breakthrough Gallade is quite good with Maxie's Hidden Ball Trick, from what I've seen. The fact that it runs off a DCE (and that the condition for getting 130 damage is really easy) means that you can put it in a deck with any Energy, and its Premonition ability is really good. I don't know about building an entire deck around the card, but it makes a very nice tech.