I have a couple of the 'cotton' vests that hold three mags and it is cheap (I'm assuming you're talking about a fancy-shmancy nylon $250 vest when you refer to 'vest'). I think it's great. It isn't in the way of a belt and the mags are easy to take out in the prone position. It's also easy to carry. They're not waterproof, but you'd be carrying them 'under' a jacket so I don't think it makes a whole lot of difference. It's the one on the bottom of the picture: http://www.pvtpyle.com/Field%20gear/ChiCom%20Pouches.jpg. They have smaller pouches 2 on each side that can each fit a 20 round box of Wolf each. Can you tell I'm a fan of this vest? I don't remember where I bought it, but you can find it easy through a search.
I bought some of those US 3 mag pounches (http://www.cheaperthandirt.com/ctd/product.asp?dept%5Fid=1240&sku=AKS%2D009&imgid=&mscssid=LKK76LQH2JPT8JVXCF262RH8NJH32B95). I am not crazy about them. They don't have dividers between the mags, so they clang with only two mags in the pouch, and it is HEAVY on a belt, especially if you have more than one. I saw this (http://www.cheaperthandirt.com/ctd/product.asp?dept%5Fid=1240&sku=AKS%2D221&imgid=&mscssid=LKK76LQH2JPT8JVXCF262RH8NJH32B95) a while back, but I haven't bought it so I don't know what they're like.