For what?
> The 6502 needs access to memory only half the time, during the what is usually called the ϕ2 phase of the clock. The other half of the time, so long as you tri-state the CPU address pins,² the bus and memory are available to other systems.
> The Z80 does not have such a well-defined, synchronous system of accessing RAM. Many cycles don't need RAM access, but many do, and which particular ones do and do not depend on the instruction mix.
> There is no "do nothing" solution to this constraint, and Z80-based systems that wanted consistent video output would have to solve this one way (hardware) or the other (software).
Ok... The 6502 does not have port-I/O. Everything is memory mapped. Therefore, the Z80 is better.
Or, the Z80 has more registers than the 6502, therefore the Z80 is better.
Or, the Z80 can do limited 16-bit operations that the 6502 can't, therefore the Z80 is better.
I'm not saying the z80 is better than the 6502, but it's a pretty big stretch to say the 6502 is better, especially if you're not coding in assembler.