I have the SR25 and Mk20 in 7.62, both are great. If you want accurate and reliable, they're the way to go. There's also LMT and HK. They're all about 1MOA factory but some can do better with handloads and literally every barrel type is present among those four.
I bet the MK20 in 6.5 would be nice but I didn't want to adopt another caliber personally. SR25 is also in 6.5 if you like and the QDC suppressor is available in both calibers now I think. SR25 also comes suppressor ready.
Surefire makes a can in 6.5 that'd be awesome for the Mk20. The new ones don't come with the barrel step down it looks like, 6.5 or 7.62, so you won't be tempted to track down legacy shit like I was. But if you suppress the MK20 you need to know that FN doesn't warranty it if you use one and that it would behoove you to get extra gas jets, a low back pressure suppressor and probably one of those silicon recoil buffers.