[anyfoo]

One thing that might or might not matter, depending on why you are doing the project, is that a 6502-based computer is less opaque.

A 6502 is a CPU in the "traditional sense". It has limited internal state in the form of a few registers, and communicates with the outside world with address lines and data lines; I only simplified a little there. Everything else is external: RAM, ROM, any external devices on a different bus (I2C etc.), even timers and GPIO need external circuitry with usually other ICs.

An AVR on the other hand tends to have all of that stuff (or at least a sizable subset) built in. That's, obviously, enormously convenient, and often means that with the AVR itself and just minimal external circuitry you have your needs covered. But it's less educational, you've rather plugged a computer into your circuit than built a computer.