In terms of combat, both Tera and Guild Wars 2 are equally good.
Tera is a bit generic on the quest-side. You just have your usual go kill monsters quests, so it's just your normal go to spawn place, kill monsters, go back to NPC gameplay.
Guild Wars 2 has a very unique quest system and has also some quite exciting aspects about them.
Tera has a higher population though, especially in PVE. GW2 suffers a lot in PVE by having hardly any PVE players left. It still has a high population but most are just doing PVP.