I play on Dragonsreach iirc and the PvE there is plenty populated enough.
Currently playing: FFXIV (Elucifer Arclight, Brynhildr server), LoL (Zacewing, NA server), SMITE (Zacewing)
OP already chose GW2, but I just wanted to add in a bit more to this conversation... The only reason to play TERA is for the action combat. The problem with that? There is a AHK script that turns GW2 into a third person shooter/slasher and if you want true action combat, don't bother with TERA. Just wait for BnS or play on an Asian server. Otherwise, TERA is a horrible generic grind fest. Possibly the worst I've played in terms of the repetitive quests.