I play MNK and BLM. I enjoy both but find myself playing BLM (until now since i just finished my Novus for MNK) mostly because it's all around better at soloing and better at aoe damage in dungeons -- also requires less effort. MNK is fun though and kind of frantic. Shaving that extra half second off the GCD due to greased lightning as well as having to move from flank to rear and back regularly makes it feel like there's a lot more going on and at a faster pace.

That said, I'd try them both out -- certainly you need LNC up to 34 either way. My LNC is 34, so I don't know how much it changes at 50, but MNK gets a very important opener at 50 which sort of changes the way everything flows for the better.