I'm pretty sure it's Triple H.
Last night was a big clue to the GM's identity and one that really threw a wrench into this whole storyline. I was running through possible names, and three came up: Vince McMahon, Shawn Michaels, and Triple H.
Vince makes sense, but it also doesn't make sense. True, he has had problems with Bret in the past (not to mention their showdown at Wrestlemania), but he was talking to the anonymous GM on the phone during the first day this business started, and as the chairman of the company he can just run RAW whenever he wants.
Shawn Michaels used to dislike Bret, but before that he liked him, and they have since made up as seen on the January 4th RAW and HBK's retirement.
Given all the clues, Trippy makes the most sense. Vince gave him supreme power over RAW, which means Vince must trust him. Triple H is his son-in-law, so of course they trust each other. Triple H was part of the Kliq that hated Bret, so that's another piece of the puzzle that fits. While the use of catchphrases is usually to throw us off, we must remember that a DX catchphrase was used, and that may be the only non-red herring when it comes to catchphrases.
The pieces just fit for it to be Triple H...
...Unless this is all a trap to mislead us and keep us guessing before they reveal that the GM is Michael Cole.