Well as usual there's a huge difference between the difficulty if doing a sufficient amount of damage to finish a heroic, and mastering it to being able to do a sufficient amount of damage to nuke heroic Maloriak's adds in time.
The generalized answer for either would be the same it's been since Vanilla: range DPS of some sort. Which one in particular changes with the FOTM. Of the most likely candidates, Beast Mastery is pretty easy to do acceptable DPS with right now, and as usual both Mage PvE specs are extremely simple, but it's difficult to put your finger on exactly one.