You are lvl 55 right?
Answer: It doesn’t matter.
You should be moving through gear fairly regularly. As you are leveling, I’m going to assume you are solo questing and doing some groups.
What I would look for would be INT (More mana = less Down time) and then randomly pick up some spell power and crit.
At end game there are definite stats to stack… (i.e. Stack Hit until capped, then stack X, then Y, then… )
While leveling, you want stack what’s best. If you get a piece that increases spell power by 15, but decreases INT by 3, that’s probably a step up… Same thing with a piece that might increase crit by 25, but has slightly less spell power than your current piece.
While at end game these considerations are made for you (Hit before Spell Power) – while leveling, it’s sort-of just a guessing game. As you don’t regularly face mobs that are 3 – 4 levels above you – HIT is pretty useless. You can get away without it. (Plus it’s damn hard to find that low)
Start to look at your gear at lvl 68. Prepare for Northrend dungeons.
(Also – start using frost as your main. It is a great solo spec.)