Personally, my preference is for GI aluminum mags.
Specifically:
30 rd mags
http://www.44mag.com/product/nhmtg_m...ar15_magazines
and
20 rd mags
http://www.44mag.com/product/nhmtg_2...ar15_magazines
NHMTG is the civilian side of Okay Industries, which manufactures mags for the Army and also Colt.
http://www.okayind.com/
I had about 100 Pmags at one time and I didn't like them that much for my usage. (Hard to get into and out of pouches and quickly wearing mag release notches, and bulkier)
Others REALLY like them, and they seem to be a sound option.