I've played both for over 30 hours each (I know not a lot when it comes to MMOs), and I can 100% say that ESO is the better game for me.

GW2 Feels like a pvp numbers game with a story tacked on, but its biggest offense is that its server vs server content is extremely unbalanced.

ESO is the most immersive MMO I have ever played. I can't tell you how many times I just felt like exploring, taking all the scenery in, listening to all of the Voice acted characters rant about my exploits. The dungeon content is extremely fun and challenging, each boss battle feels different from the rest.

GW2 Dungeon bosses all feel the same, and I can just spam attacks until I win. Meanwhile in ESO I'll sometimes be frantically freeing our tank from chains as a massive ghost sword slowly drifts towards the tank's body threatening him with a one hit kill unless the team removes the chains in time. It's frantic fun.

GW2 is a numbers game, and the game just gets tedious even before and after max level. ESO is on a whole other level, it's immersive, beautiful and feels more like I'm stepping into another world for a few hours rather than playing another grindy MMO.