I'd say Donphan is the dominant deck right now. It's had a big presence at Cities, and has claimed a stellar amount of victories. I made top eight at the Cities I went to today... and exactly half of the top cut decks (including my own) were Donphan. It's a strong, balanced deck that handles most of the common threats rather well. Yveltal has a hard time keeping up, especially if the build is EX heavy, but builds running high counts of Yveltal XY give Donphan a hard time. Donphan can also overpower VirGen if it sets up fast enough and makes critical KOs in a timely manner. Even Seismitoad has a hard time outdamaging out, and Pyroar struggles to trade prizes.
What's real interesting about Donphan is that most builds run no Pokemon-EX at all, and the ones that do only run a single Landorus, Seismitoad, or possibly Jirachi. This forces the opponent to take six prizes the hard way, which in an EX-heavy format, many decks lack the resources to do efficiently. Decks like Seismitoad and Yveltal that rely on Laserbank to boost damage can run out of resources quickly, especially when they need to maneuver around Safeguards, Outragers, and Robo Substitutes.