Decks that are going to see play at Regionals:
-G Decks (variations of sorts, both Palkia and Dialga)
-Machamp (After all, it's a good play vs. G's for the most part)
-Gengar (With all the new trainers that entered the format, including a supporter that lets you look at your opponent's hand, Gengar got a lot better, not to mention Shadow Room is a good attack as well)
-Tyranitar (Whether you play a build that is based more along the lines of Grinding and Tanking, a build around Spinning Tail spread also isn't a bad choice. With Blissey PT you can heal yourself and discard basic dark energy, this is going to be a powerful play at Regionals)
-AmphyTric (Though many have forsaken it and thought bad of it, if it sets up quick enough, then it can be a powerful force, by locking powers with Damage Bind, starting the lock with Jamming, and preventing spread with Electric Barrier, this isn't a bad choice, just be careful and play smart against Dialga as your bodies are locked, and don't for your Blissey tech and/or Potions)
-AMU (Quick, Powerful, but once against rusty vs. Dialga. It needs it's trainers and stadiums to set up to win, and with Dialga locking those, that becomes a problem, however it is the same with AmphyTric, just attempt to set up the quickest you can, hope they whiff start, and go for it the best you can)
-Regigigas (This big tank IMO is still in buisness. Since Trainers are not essential for it's set up, it can still set up while being Deafen locked. It has no bodies that are essential either, meaning vs. Dialga you don't have too many problems, however Palkia will give you troubles with chain power lock)
Those are some of my top picks for Regionals