What is a "good" assembly language? The best I've ever seen was the VAX instruction set. The second best, probably m68k. These were big, CISC CPUs that were as nice as possible to program in assembly language.
The 6502 wasn't. Everything about the 6502 was "do more with less" and you had to be really clever to eke out performance on it. But that's a good thing! A clean, big CISC architecture like the former ones is also a good compiler target. The 6502 was deeply weird, but programming it in assembly was necessary to get it to fly. That's an era. If you want to relive that era, then go for it. It's much more quirkily fun that, say, the 8080 (the Z80 is another beast, though backwards compatible) and much more mainstream than the otherwise better 6809, all of which are also from the "assembly language required for performance" era.
Arguably PDP11 is probably the best. Dates back to the assembly language programming era, but nice clean instruction set. But what are you going to run your PDP11 code on? A simulator? Sure. But no real, consumer facing machines with graphics chips.
If you like the PDP11 instruction set, then you'll probably enjoy 68000 as well. It drew a lot of inspiration from the former. You lose the "deferred" addressing modes (though the 68020 adds something similar), but gain access to a few other useful ones. Conveniently it was used in a lot of consumer devices (Mac, Amiga, Sega Genesis, etc.)
The 6502 wasn't. Everything about the 6502 was "do more with less" and you had to be really clever to eke out performance on it. But that's a good thing! A clean, big CISC architecture like the former ones is also a good compiler target. The 6502 was deeply weird, but programming it in assembly was necessary to get it to fly. That's an era. If you want to relive that era, then go for it. It's much more quirkily fun that, say, the 8080 (the Z80 is another beast, though backwards compatible) and much more mainstream than the otherwise better 6809, all of which are also from the "assembly language required for performance" era.