Could you explain why? I have quite a bit of experience with Z80 and x86 (16bit) assembly. I remember that I've tried to learn 6502 many years ago but lost interest after a while. I remember that 6502 didn't feel superior to me then, quite opposite.
It's extremely simple. It's too simple for modern use, given that it doesn't have 16 or 32 bit instructions and lack mul/div etc., and doesn't have a decent sized stack, but for a small system like the C64 the simplicity was great - it was easy to learn, and for things like demo programming it's easy enough that you can quickly learn to remember how many cycles each instruction + addressing mode takes.
If someone where to build a machine like that I think the 8080 (or at least the z80, which is still manufacturered) would probably be the best choice. The Intel 8080 is very clean and well thought out compared to the 6502. (try writting an emulator or assembler for both)