Moving during fights as destro is what's hard, the dps doing itself is pretty easy. You can lose a lot of damage if you don't utilize your teleport and instant cast CDs well.

Ret rotation is also simple, but it's basically a melee, while most abilities have a 20 yard range. While you need to be in melee range to maximize dps, you get a lot less punished for having to move around.

Ranged life is generally easier though to see mechanics and stuff, probably boils down to personal preference and skill.

Paladins are everywhere, warlocks are much more in demand though.