I voted for tailoring. Why? Because, as it's been said, it's far more expensive to level tailoring via the AH than it is to level inscription. Boniggy was nice enough to share his profile with me that leveled me from 1 to, roughly, 450 (maybe a little higher, can't remember anymore). It cost me gold because I was lazy and didn't want to farm up the herbs to have a friend of mine make the inks. Basically, I bought all the inks I needed, somewhat cheaply, and it ink traded, trained, made glyphs, etc. It was pretty nice, and worked quick as hell. It only took me a couple of hours to almost max inscription. Anyway, I've leveled every professions in WoW right now, except tailoring, and I'm doing that by hand. It's a pain in the ass due to all the cloth / volatile requirements. Once you reach frostweave and embersilk, be prepared to farm your ass off. FW needs ~1300 pieces of cloth, and ES needs ~1750 pieces of cloth, and ~500 of each volatile ... that I can remember. I could be wrong about the vols, but I do know for a fact that the ES section requires a ton of them.
In my opinion, tailoring has been the worst to level so far.