Well Magpul does make the best stocks for AR's (i am an AR guy), so i imagine since the stock itself doesn't change, just the weapon, Magpul would be one of the best choices for the 556 unless you prefer the SIG side folder....im a noob with the 556 but i heard the ACE side folder with Magpul CTR is a nice setup (folds to left or right depending on how its set up on your weapon---so you can fire it if need be with the stock folded to the left)...i am in your boat too and don't know what stock to go with yet...i may wait til DDLES releases their adapter for the stocks and get a magpul acs....i WANT a folder, but i dont think i NEED it....