Arcane/Frost, but mainly arcane (call me crazy, but I'm more comfortable with arcane rotations).
To me, Arcane's rotation isn't difficult. The challenging part for me when I Arcane is mana management and limiting movement, which is why I don't play it right now. Also don't know how Arcane mages will do on fights with heavy movement in 5.2 without Scorch.
I'm so used to never running out of mana as Frost that I've stopped making Mana Gems and removed the skill from my bar altogether. The only time my mana pool takes a dent is when I'm spell-stealing Cleansing Waters from the Protectors in Terrace (because for some reason healers can never dispel it fast enough so I always steal it away). Even then, it's nothing an Evocate can't fix.
Fire's rotation is also easy, the only thing you need to properly time is Combust, but Fire for me is gamble based and I don't know why I get so many cold, non crit streaks as Fire even with a spell crit of 32%.
Frost's rotation IMO is the most clunky, especially with Freeze being an AoE but being in rotation even on single target. Although I'm glad it will be out of rotation on some boss fights in 5.2, I really think they should have given us Water Jet or another replacement spell to make the pet more interactive.