Based on my experience building custom rifles full time for the last 10 years I can say the brand with the lowest failure number has been Nightforce. And I sell more of them than any other brand. I just don't like how NF handles issues. They say theres nothing wrong with the scope and it comes back fixed. As far as scopes go Ive seen every single brand have an issue. Some alot more than others. I won't offer an accuracy guarantee with leupold or vortex. Most of what I build is lightweight 30 cal magnums. Your 15-20 lb 6.5 creedmoor won't have issues with most decent scopes out there. For all my personal hunting rifles I now have Nightforce 4-20 ATACR on them. The durability of it over a Tangent, ZCO, Kahles, swarovski etc far outweighs the slight difference in optical clarity. I haven't personally had or had a customer have an issue w a ATACR yet. ZCO can take some abuse but Ive had the parallax go out on a few of them. Most of those issues were with Spuhr mounts. Tangents had the same issues in Spuhr mounts. Im not a fan of spuhr mounts as they clamp the scope too close to the turret housing. Had a combination of 7 tangents and zco that went out on spuhr mounts. If you torqued the rings to spuhr spec there was issues. Theyd still slip and cause issues w the scope in big lightweight magnums. So I bedded them into the rings and torqued them down. They didn't slip but still had issues occasionally so I don't use those mounts anymore. Haven't had any issues yet bedding a ZCO into the ZCO rings. I did have a windage turret freeze on my Tangent Marksman 3-15 when it was single digit temps. Brought the gun back inside and a few minutes later the windage worked. Brought it back outside and a little bit later it froze again. Scope was bedded into NF 6 screw rings. Tangent sent me a label and I had it fixed and back in a week. Their customer service has been stellar in the few times there has been an issue. Same with ZCO customer service, top notch.
I also have a scope tracking jig to see if the reticle will move due to recoil. Most scopes will allow the reticle to move due to recoil. Ive seen some move 1/2 moa in 10 shots. NF NX8 and ATACR, ZCO, Tangent, Swarovski, and kahles pass the reticle movement test. Others I have tested do not.