It sounds like you've already made up your mind and are just asking for confirmation. A lot of the enjoyment of GW2 centers around PvP and that's where it really shines. WvW is oodles of fun if you're in the right mindset, and it doesn't "play" like traditional PvP - you might enjoy it, but I don't have enough information to know. If you're looking to make a bad ass character that is stronger than other players, it might not be the game for you. It rewards skill and creativity over superior stats.
As you said, you know what you're getting with WoW. The game is practically ancient by modern standards. If you enjoy that, then by all means go ahead. You probably won't be disappointed. However, I'd suggest finding a way to give GW2 a try. You might be delightfully surprised. There's also the subscription fee to consider, which GW2 does not have.
All things considered though, I'd say MOP is probably going to be the better buy for you. Late game PvE and character building is fairly weak in GW2, so I wouldn't purchase it exclusively for that. But I really do want to again urge you to give it a whirl. I think WoW has rigidly defined the MMO crowd's expectation of what a MMO should be for the worst. Personal opinion and all that.
