In short, US made surplus is fine, but I would avoid foreign made surplus unless it from a NATO known manufacturer of good ammo, for example Portugese .308 battle packs are excellent quality and still priced good. The Indian made .308 for instance is crap with weak brass and frequent case separations occurring.
Ammo from european countries with NATO headstamp is usually OK if in origianl packaging, so you know it's all original.
I shot nothing but Portugese made NATO 7.62x51 ball out of my HK91 when I still had it, never had a misfire or issue with it, I must have gone through three or four cases of 1000. Cheaper than dirt used to have this in 200 round battle packs (OD green heavy plastic hermetically sealed packs with carry handle - you could keep it in the pond outside for 10 years, pull it out, and shoot it)for $29.99 each. Excellent ammo at that!
Now to just find a range that allowed FMJ, that was a different story....
edited to add: looks like they no longer have the portugese but they are selling NATO spanish made .308 by the 20 rnd box for $3.89, thats a good price, and Santa Barbara is good ammo. Brass case, berdan primed, non-corrosive.
http://www.cheaperthandirt.com/ctd/product.asp?sku=AMM%2D693&mscssid=HPXCFCKSNUW18LVNG306HUAEXFKGDS57