My friend is working on goldsmithing, so i was gonna avoid that one.
Sucks, cuz I'd say that's the best one at least for Leviathan.
From personal experience, I'd recommend Leathercraft or Clothcraft.
Why? Because they are the easiest to get ingredients for.
Leathercraft: Most profits come from accessories, but they are cost effective and can mostly be farmed or cheaply purchased from AH. Additionally, you can profit from the Faulpie Leathers alone (again, server dependent, so check that)
Clothcraft: Even easier to farm ingredients for, and tend to be profitable on ingredients alone since most are for upgrades or other crafts. Used to craft important mage neckpieces, and also profits from accessories. Only downside is the Weavers' Torque is a pain in the *** to farm. (I'm 0 for like 1k boxes I swear and at least 48 hrs of non stop farming)
Both of these are also efficient to level.
I'd not recommend Alchemy or Woodworking, since their ingredients can be a pain to farm, although are fairly profitable as well if you can get them high enough. Alchemist Torque is also a huge pain since it isn't effected by the Kupowers.
I hope this is useful for you ^^