I have a Leupold Competition x45 on my BR rig, some guys at my club are shooting March and NF, i haven't looked through any of them and felt the need to change.
The Leupolds are maybe a bit old fashioned now compared to newer offerings but all the better for it IMO and can be picked up for sensible money.
I have a Weaver T36 on my LWSR, its a bit dark and for me the mag is a little on the low side for BR but a few guys at the club use them for BR and rate them.
We did have a few using Sightron but all have moved them on after various problems.