Agreed on 20s being nice for bench and prone. I like p mag 20s (G3) but also have pmag 30s (G2 and G3) and aluminum GI (D&H and some miscellaneous) 20s and 30s.

G3 pmag 20s are my first choice.

Best deal around for pmags:

https://www.provenoutfitters.com/pmag-20-ar-gen-m3-5-56x45-bk

My understanding and experience is that any modern twist (1-9" or faster) will easily stabilize 62g green tips. A 1-12" might have trouble, but I don't know of any 1-12" AR barrels except some "retro" reproduction barrels and old surplus