I've raid led as every role, and generally I'd say that they're all more or less equal, except as a healer I have to dedicate my focus target to the boss so I can see his casts, energy, hp%, etc. The simpler a class is to play, the easier it is to raid lead, obviously - there's a fairly big difference rolling my mousewheel up and down on my guardian vs watching 4 debuffs, 2 buffs, 3 cooldowns along with managing combo points & energy on a feral.
I think the reason why a lot of tanks are raid leaders isn't because it's easier to RL as tank, but as RL you gravitate towards the tank role, because you're more aware of the entire fight than the average raider which allows you to perform your tanking duty better than someone who only pays attention to tanking. I know it's aggravating telling the tank to do move a boss over that way or telling him he died because his healer moved out of range and he wasn't paying attention, whereas raid leaders are usually more cognizant about such things and would just automatically move the boss because it's the optimal thing to do at that point, and they're already aware of the surroundings and will notice that their healer is high tailing it out with a frost beam or something.