After having played both of them
[Also I'd like to mention that I purchased both, GW2 AND TERA!]
I find GW2 better overall. The only thing superior to GW2 in TERA is the combat. And perhaps the graphics overall. Though GW2 graphics are gorgeous too.
GW2 is more engaging, and has more content. It just keeps you going and motivates you and it's seriously high quality.