I use Millet 34mm low rings on a Bush. XRS & DMR.
I think they're very solid rings, very square/true to my surprise. Got them 2 or 3 years ago at opticsplanet.com for like $50 a pair !, but I don't see them there anymore. opticsplanet has a HUGE selection of rings and some of their prices are hard to beat.

My second choice would be the Burris XTR SIGNATURE rings with the moa offset inserts.

If you have the money, get a SPHUR mount like their SP-4901 model !

If you're using a 20moa pic rail, I think all low rings will work because the objective bell will be overhanging the rail like mine do. Just make sure when you mount it, the objective bell clears the rail

If you're rail is very long, then you'll need high rings. Or you'll need to cut the front of the rail.