I just use the H buffer for the most part, although I do have a Spikes ST2.
I have used a variety of muzzle devices, and the favorite so far has been the AR Stoner Competition, which is pretty much the same as the JP Comps, just cheaper, and I just picked up an Arredondo comp to try, which I also think will work well. Have tried the Troy Medieval comp and its ok.
Agree with what Bert had to say, the buffer has more to do with the cycling of the rifle, the comp, rifle weight, stock fit, and ammunition selection is what affects felt recoil.