I believe 6502 instruction set is a good first assembly language

Zero page is like a having 256 generic RISC registers (a bit faster than accessing to other memory areas).

Very easy to understand how the assembly is micro-coded

Cons:

It is impossible to create a "generic" memory pointer with an index >255 without auto-modifying code.

It is a true 8bit only system and cannot manipulate 16bit word easily Steve Wozniac created a small VM just to manage 16 bit Integers (see the his Byte magazine articles).

Too much addressing mode.

So I like 6502, but I disagree a bit.

I studied electronics, so naturally we began with assembly (Motorola HC11). By the end of the course everyone had independently developed their macros to do things like for-loops, so it was a natural progression from there to C. By the end of the C course "C-style OOP" had also emerged naturally, which led to the next course in C++.

The downside of this approach is that it there is no gradual route from there to functional paradigms (or non-imperative in general). Also, one develops the habit of always thinking of how the language works under the hood, which can be counter, productive. E.g. when I was trying to learn Haskell, my mind was trying to understand how the interpreter worked.

Learning assembler is not just about the language, but understanding how the machine works (buses, memory-mapped peripherals, etc). In older platforms this is much simpler, so while ARM instructions can be easier to learn than the CISC instructions of the HC11, everything else is much friendlier for the beginner in the HC11.

https://store.arduino.cc/products/arduino-uno-rev3

are affordable and have good tooling. Memory capacity is tiny but it is fast, andthere is a lot of I/O, you can even write console programs that use the serial ports or better, programs that do physical things and also communicate over the serial ports -- in some ways AVR-8 boards are more capable than conventional computers, phones, etc. So far as I can tell, AVR-8 was the last 8-bit architecture, if it has a real weakness it is that, compared to other microcontrollers, it's a dead end because you're going to upgrade to ESP-32 or ARM if you need more.

The 6052 has more registers than the PDP-8 but just barely. Writing compilers for the 6052 is difficult because there just aren't enough registers not to mind a limited set of addressing modes. If you want to do anything interesting with the 6502 you are likely to use virtual machine [1] techniques such as Wozniak's SWEET16 or the atrocious UCSD p-System [3] or Infocom's Z Machine [4]. That kind of stuff is really fun, but so is writing straightforward AVR-8 code.

I have fond memories of the 6809 which supported really advanced software engineering techniques at the time [5] but if I had to pick a classic 8-bit architecture that is easy to find hardware for today it would have to be the Z-80, or the successor eZ80, which I think the only 24 bit micro that didn't suck (had real 24 bit index registers!) Boards are available [6]

[1] as in 'Java Virtual Machine', not 'VM/CMS'

[2] https://en.wikipedia.org/wiki/SWEET16

[3] http://pascal.hansotten.com/ucsd-p-system/

[4] https://en.wikipedia.org/wiki/Z-machine

[5] https://en.wikipedia.org/wiki/OS-9

[6] https://www.olimex.com/Products/Retro-Computers/AgonLight2/o...

The 32-bit ARM ISA, yes, but ARMv7 came much later. You're basically limited to ARM2 on the Archimedes, according to https://en.wikipedia.org/wiki/Acorn_Archimedes

In the context of someone's first contact with assembly language, that's a good thing! Translating various multiplication and division algorithms to assembly is a great way to learn it.