Running an Eagle drive train then you need an Eagle chain. The X01 in my mind is the best bang for the buck for durability and reliability in the long term. I have found in my experience that the X01 chain has much tighter tolerances than perhaps other chains. I actually replace mine at the .5 wear indicator on my chain checking tools and not the .75 or 1.0 as I would on my old 11 spd chains. I feel the chain is still wearing out in the same fashion it just starts out tighter.
I use the PARK TOOLChain Checker - CC-2 Item # PAR0055
Fantastic quality from SRAM as always. Haven't had to deal with any breaks thus far, and installing it was easier than putting butter on toast. If you're in the market for this type of chain, this is the one to go for.
I love Eagle, and the best way to ensure you don't have to buy a new $400 cassette is to replace your chain before it gets too stretched. I typically spin at a higher cadence so my chains tend to last, but I still replace them every 600 miles or so on the mountain bike just to extend the life of my cassette.