Upper Guk and Unrest are probably THE zones to go to, both have nice exp modifiers on them. Unrest for me is slightly more noob friendly, I get lost in Upper Guk quite easily but when I have grouped in there it's been good
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Unrest is popular, doesn't take too much to get a fireplace group started though it's usually fairly quiet during the offpeak hours.
Those two aside, Highkeep is always an option - should be plenty there to pull, vendors and bank right there, and fairly easy for people to get to.