GO- NO COMMUNITY! i advise you stay away. fun at first but get's old quick. you mite as well play maplestory if that's what you're looking for.
CT- don no, never played it.
Lunia- it's pretty fun. It's realy story oriented. It's arcade style hack and slash. it
's ok cant play it cause it laggs on my comp but u played be4 the updates. This one's worth a try.
Zero- It's also pretty fun. Iso robot game. It's good and moderetly fast pace. more of a traditional MMO.
i personaly would want to play either Zero or lunia....yeah lunia. it's not the best in the world but, it's the best on your list.