Demo in early Cata probably had the most complex rotation in the game, but it's much easier now. The difficulty of Demo comes with managing fury and the Meta toggle with your cooldowns. The difficulty of Aff comes with managing all your procs and cooldowns to max dot refreshes. Not sure how you can compare the 2. For me, I don't play Aff because I absolutely hate the idea of managing all those random procs. Not sure if that makes it harder than Demo.
I actually think Ret has a really complex priority system with all the different timings. But there's the CLCRET add on which turns it into one of the simpler rotations. I wouldn't enjoy playing Ret very much without CLCRET.