WoW classes typically have a lot more abilities to juggle than in LoL. To play well with most classes, you need to utilize most, if not all abilities at an individual level. LoL on the other hand has fewer abilities. I would say based on that alone, LoL is less complicated for the player.
That said just because something isn't complicated, doesn't mean it doesn't have depth. LoL has a lot of depth. You don't often see it in normal games, but watching the pro-games and the way teams work together with an almost synergy of using their abilities is awesome. Being aware of where your enemy is on the map is key. They don't typically conform to standard item builds. Same can be said for WoW as well really.
On a personal note, i prefer LoLs approach. Less abilities and more about timing, planning and execution. WoW PvP really has become burst person x down while they are chain CCed and can't do anything. You don't even have to time your CCs right anymore.
Both PvP communities are toxic though. LoL being the worst by far.