The 787 CS has the seats angled differently - in effect they are straighter to compensate for the narrower cabin. They look less spacious on the 787 (I haven’t flown in one only walked past them) due to the reduced overall seat space width however I get the inkling that the screen is further away from the seat - by a bit - which if true means that your legs are not in a foot coffin as much as on the 777 (which isn’t bad at all in my experience).

Overall if I had a choice I would pick the 787 CS because of the higher air pressure, the use of fresh rather than engine bleed air for cabin air supply, less noise and bigger windows.