I originally bought MDT rings for my DMR2. Unfortunately they were out of spec ('bores' measured oversized when completely bottomed out, scope slipped) and I had to send them back. A lot of other people have had no issues with theirs, so it seems like it's maybe just a case of my typical bad luck..... *shrugs*. Due to them not knowing how long the next batch was going to take, I replaced them with Nightforce rings instead and have had no problems with those.
The nightforce were more expensive, however. ~$300 compared to ~$230 for the MDT. Seemingly, a lot of people have good reviews of the ATRS rings, and I've never heard anyone complain about Badger rings either.
A few companies are going with the 'near-zero-gap' method of ring manufacturing, to help prevent scope tubes from being crushed via over-tightening (or from scopes with thinner than standard tube walls *coughvortexcough*

).
Personally, I use a torque driver anyway, and have never had an issue crushing scopes, so gaps aren't really an issue for me. YMMV.
If you wanna go 'drop-out-of-a-plane' overkill, go with sphur. They have some neat features, and speaking from a machining standpoint, they are a work of art......but they are also a lot more expensive.