It all depends on what current gear you got..
I spent my first on totem, simply because the shaman elemental totem in pretty insane. My next, I spent on shoulders. My choise there was because I'm still only doing Heroics, since i don't have any other boxer to raid with me atm. (Ele shaman shoulders don't have hit, but haste/crit)

It all comes down to simple math if you are looking for the 'best' upgrade. The ring is also great for casters, seeing there is a lack of good caster-rings before raid, atleast besides the TOC Heroic ring. (31 runs, 2 rings so far.)