Depending how often you play, and when GW2 comes out, if you choose BLU you might still be getting spells for it when you leave, so I would leave that for now.
BST can be a brilliant job for soloing just about anything once you build up your gear sets.
NIN/DNC is good for both solo and groups. Can be quite costly though, especially for a newcomer. (On BST you would be able to get at least 100 currency from dynamis every day to sell)
SMN is very useful in some of the more challenging fights in the game (Arch dynamis lord etc.) but you need to get alexander, which means doing the aht urgan missions first.
DRG is a nice all-rounder, not especially asked for in parties, but useful for both healing and DDing.