Atari 800 vs Commodore 64
Atari 800 was one of the best 6500 systems.
Better than a Commodore 64 in many ways.
The greatest advantage of Atari 800 over C64 was expandability.
800 had multiple card slots.
Later Atari XL/XE were worse by loss of expandability.
Atari was faster, its 6502 ran at 1.7Mhz, C64's 6510 ran at 1.0Mhz.
Atari's graphics had more more colors (base colors plus luminance levels)
and more graphics modes (resolutions).
Graphics chip of Atari (ANTIC), like Amiga, was a coprocessor
that executed "display lists". Mixed modes were coded in Atari
by 6502 placing into RAM "display list instructions" for ANTIC to execute.
Atari had a smooth-scrolling of its "playfield" which C64 had no counterpart.
C64's sprites were better, the only area in graphics C64 had an advantage.
Atari's "player/missile" sprites had limitations in setting positions.
C64's sprites could be set in any position and were larger.
C64's sound was far superior with its SID chip.
For a user interested in music, C64 would've been a better system.
In games that were ported to both, C64's voices almost sound like real musical instruments,
while Atari's voices sounds like a primitive synthesizer.
Atari BASIC was better, having Atari-specific commands, and may have been faster.
Atari had its own DOS and could boot into a useful notepad program.