Obviously playing one class is easier than two, but the difference is minimal, especially if you're only playing two characters. Heck, when I first started I was using three characters, two of which were melee(warrior + paladin), and I had no problems aside from it being annoying getting them both in melee range. The reason I suggest using different classes is because it isn't much harder while it gives you a lot more options. Obviously some people may prefer using all the same class, but someone new who is asking probably doesn't know what they want, which is why they are asking in the first place.

By the logic of CC > everything else, mages would be by far the best class to use. I'm not arguing with that, but it isn't going to hurt much to have two sheeps and something else. You need to gauge which you think is more important for your group/playstyle, that extra sheep or whatever the other class brings, whether it's a soulstone, extra healing, buffs, off tanking, or whatever else they may bring. The problem with rogues is the amount of micro they require, not the lack of other things.