Depends what you want to get out of it. If you want equips, go with the craft that will give you the most. If you want stuff to play with, go engineering(like a cool flying mount!). If you want to make pots(or help pick up the mats for them) go alchemy/herb.
If you just need more money(for you know, looking at), level enchanting and disenchant cheap greens at the AH.