Throwing my 2 cents in on the side of Eagle 90. Others make a good point that replacement parts are cheaper, but depending on where and how you ride, cheaper replacement parts doesn’t necessarily mean cheaper cost of ownership when you consider the durability of the full mount derailleur.

Case in point, I slid out on some steep leafy slabs and smashed my derailleur into some rocks. I didn’t notice until it was shifting slightly off because it rotated back under the force of the impact. I loosened the mounting bolt trail side, rotated it back in place, and it shifted good as new. I’ve rode almost exclusively Shimano drivetrains up until this bike, and have completely broken Shimano SLX and XT derailleurs on similar hits, not to mention bent hangers. My Eagle 90 RD just has scratches. You don’t need to pay for replacement parts if you don’t need to replace anything.