Guild Wars 2: Still has a somewhat active community depending on which server you play on. As long as you join a high-populated server, you'll be good. The combat is pretty fun and I personally found questing to be enjoyable. The dungeons themselves will take a while depending on whether someone in the group knows the fights and can explain them. I played the game at release and I remember spending 3+ hours on a single dungeon. That might have changed though. Questing is your typical 'Kill X, Go to Y, Gather Z' but you find the quests on your own. It's not like most MMO's where you go and talk to an NPC to get a quest.
World Events are one plus to Guild Wars. There will always be big enemies to fight that must be fought in groups.
If you're into customization, you can collect dye and customize the color of your clothing. Trust me - There is a shit ton of dye in the game and it can be pretty fun to mix and match. Personally, I liked matching my clothes to the environment of the area I was leveling at that moment as it made me feel more immersed in the universe. Now, you might be thinking, "Clothes? That's silly." Trust me, when you enter a new zone and you just listen to the in game music, you'll want to be as involved as possibly. The OST for the game is simply beautiful.
PvP is pretty friggin' big, obviously. Find a good world and you'll have a good time fighting against other servers. You can also do arenas with other players if you're into that sort of stuff.
Also note that Arenanet adds content every month or so, so you'll always have something to do. Another plus is that the game has no monthly fee. I rarely play it but every now and then I get on and do a few things here and there. It's nice not having to pay a fee and get on whenever you want.
World of Warcraft: WoW is in a pretty good spot right now. There is always something to do. They have pet battles (it's like Pokemon), PvP, Arenas, Raids, and a bunch of daily quests that you'll eventually grow to either love or hate. Or just hate. Each class is fun and plays entirely different. Each expansion zone has a lot of content. The community is alive and kickin', and Blizzard has pretty much made everything as accessible as possible.
I could honestly go on about both games.
WoW has a monthly fee but has more bang for your buck. It's a very nice place to start off if you've never played an MMO.
Guild Wars 2 can feel a bit more hardcore at times and has no monthly fee.
WoW will always have a large community, especially with expansion being released next year. GW2 will continue on as long as Arenanet continues to put out good content.