Are you considering just UHD sources or also HD/SD? The lack of Dolby vision on Apple TV would mean using oppo for those films at least.
There is also this thread: HDR metadata not correct, replaced by standard values
But otherwise it would be nice for someone like Vincent Teoh to do a comparison of Apple TV HDR vs Oppo. I enjoy movies and want the best quality myself but don’t have the expertise to really tell all of those details.