Gallade & Gardevoir, G&G. It's tough, that's for sure, but it's boring and very overplayed.
Magmortar is much more interesting, since you can use many different strategies and still be great. I like cycling Arcanine SW and Mag. LV.X's Flame Bluster is basically an instant prize. Ninetales might be cool here too, 2 for 60 and discard one... Better in Typhlosion though.
Infernicatty is neat, filling up the discard with Fire energy by means of Delcatty and Infernape, then Infernape LV.X comes with a big 150 and puts 8 back in your deck. Dwnside is, you need 8 energy there to use it.
I'm thinking up my own Sharkario deck type, Lucario and Sharpedo as the stars... It'll be expensive to make though, since I can only get cards from boosters where I live.
Blissey decks are good, but I'm not too familiar there.
Houndoom is just sinister. I'm definitely working on a Houndoom/Darkrai deck, trying for 80 dmg on turn 2 with burn.