TT can be nice if you know how to efficiently run it. NS is ok to farm solo at certain times, other times you will need faction/friends to help (nighttime on server is pretty quiet in there). As for warsong I would say nice to be able to farm if you can multi-client/have friends who can help ... but I lose my patience for it xD.
I would say most guaranteed way is NS but you obviously risk the chance of losing your coins.