Tons of threads on this topic, please use the search function.
My experience and results from hundreds of actual measurements of the impacts of diffusion vs. absorption lead me to recommend absorption behind the speakers if they can not be pulled out enough.
If doing multichannel (music OR movies), then absorption is your friend, as it really helps deliver a cohesive soundfield. It also really helps fix the head-in-a-vise problems that excessive sound coming from the side walls creates.
Sometimes, some diffusion helps in very specific locations, and I have some on the back wall of the dedicated room.