I think it'd be hard to find someone who doesn't think PMags are at least a decent if not excellent choice. The only downside to PMags I've found is that they tend to be a bit wider and may not fit in all mag pouches.
USGI mags can be good, especially if they're new. Older ones that cause problems are often fine if you just download them 1-3 cartridges.
I bought some cheap $5 Thermolds at one point and they are kind of iffy. I'll use them at the range for drills that involve stripping a mag and tossing it to the ground (especially for practicing type 3 malfunctions or emergency reloads) to save the abuse on my good mags.
I also like having a few 20 round mags on hand for shooting prone.
