The big pro of the Ataris was their graphics. Replacing a frame buffer with a display list and a dedicated processor that keeps banging out pixels based on its "program" is brilliant. It's an interesting maximalist counterpoint to the Apple II's minimalist approach to color graphics.

The C64 definitely had better sprites and music, no contest. But there's a certain elegance to the way the Atari did their graphics in particular. It was so much more with simple building blocks where you could immediately see the power of it and take a long time extracting value from it.

The SIO of the Atari is also another standout design, which flies under the radar. It enabled a much cheaper diskette drive than the C64. The designer of the SIO, Joe Decuir went on to make USB and credits his work on SIO as the basis of USB[0].

Even the use of letters for devices was already ahead of DOS with D: being for diskette, but that was shorthand for D1:, with D2: being another and any other letter could be an installable device with numbered instances. Keyboard/screen I/O was addressable as E:.

[0] https://en.wikipedia.org/wiki/Atari_SIO

It’s a bit like an early GPU.