A 2 Stage is generally better for an AR for at least 3 reasons:
1) It has a lighter safe final pull weight.
2) It is safer with a lighter final pull because it does a better job of preventing bump fire type inadvertent shots and slam fires (This gets more important the heavier the BCG is, for example in AR10s, SCAR-Hs, etc).
3) It gives better ignition because you can have a heavier hammer spring and still have a good pull weight.
