Spuhr is a great mount, I love mine. I wouldn't hesitate to buy another, but Any quality set of rings will get the job done. (NF, USO, Badger, even the Burris XTR rings are pretty good)

You'll have no problem getting a zero @100 with a 20 MOA mount on an AR, I run a 20 MOA Larue and have no problems getting a good zero.