The C=64 had a dumb frame buffer for video, while the Atari 8-bit had a display list processor that let you change the video mode scanline by scanline, and pull frame buffer information from several locations.
The atari 8-bit engineers were the ones who went to Commodore to design the Amiga, while the old CEO of Commodore went to Atari to build the ST as a 16-bit C=64.
So:
Atari 8 bit > Commodore 8 bit
Commodore 16-bit (with Atari engineers) > Atari 16 bit (with Jack Trameil from Commodore running Atari)
(From a programming and technical standpoint, though in terms of sales I believe the C=64 and ST won.)