Q u o t e:
Unless you will never level another character after this, you may be better off with the cloth +10% XP items. I made the mistake of buying the plate shoulders because i was leveling a paladin and a deathknight, but now that I started a shaman I need to buy new ones. this time I'll just go for the cloth version. Leveling is asy enough that you can survive with a few cloth items even as mail or plate user, in my opinion.
Unless you have enough to buy a cloth, leather, mail and plate set, of course. I that case get mail for the shaman.
I did something similar. I bought the leather chest and shoulders for my rogue, but then also used them for my retribution Paladin. I bought the cloth chest and shoulders for my warlock, and am now using them on my shaman.
Okay, stats aren't always ideal for each class, but +Exp is universally useful to all characters under 80 ;-)