Okay so Ill walk through why for what slot, even if im just supplementing others:
The first decision for the ally shaman is gloves/feet. Whether to use wc/sfk leather or cloth gear with more int. Obviously it comes down to how much hit you need, but armor is also a consideration.
I like my set because it has the exact amount of spirit required to cap, without sacrificing too much int or crit or stam.
On noble robe v. pve mail: Again i dont think the sacrifice of stam, int, armor is worth it for ally, it certainly may be for a hordie who can reach higher crit rating.
Both factions have a lot of choice for rings. I use the default int/stam rings that most people do, but good alternatives are: dpr, lorekeeper, wc ring, stendels, dm ring.
edit: On head: lfh is good style and stock shield is more armor, but for a headmasters charge ele yes eye patch would be better. You gain agi and more room for int and crit, where hit cap is automatic. Ill say that if i made my shaman when boa shields were available, i would have taken eye patch. But again, preference, and don't forget style.
edit: On bracer: Obviously mtb if you can lucks, rfc bracer is fine because it has some spirit, but I would find 3 spirit elsewhere. Owl bracer chanted plus 1 spirit would be what i used without mtb. Again, sfk bracer for straight crit.
Making a full crit ally sham is viable, if your heart is set on it, but its a lot of work. namely: pve staff over mace/shield, pve shoulder, eyepatch, dpr, stendels, 2x int trink. With some variations to the current accepted bis, ie: crit/agi bracer/feet.
My advice when gearing is to try to hit thresholds or min/max values for stats that aren't considered primary, but are necessary: hit rating, stamina, spirit, armor even.
Everyone will have different quest rewards or different world drops, but as long as you meet some minimum values, your toon should perform just fine, after that the theory crafting is only secondary to your skill set.