Interesting question...
I would call the A1000, A500, A600 and A2000 16-bit machines as they have a 16-bit data bus. Their architecture is 16-bit as well.
The AGA Amigas are 32-bit as they have a 32-bit data bus. I think the AGA chipset also makes use of a 32-bit data bus, making these models true 32-bit.
I don't know how to classify the A3000. I think it had a 32-bit data bus, but the chipset only used 16-bit.
The 68k CPU used to be called a 16/32-bit CPU, so maybe one could call the non-AGA models as 16/32-bit computers, even though it sounds clumsy.
Cheers!
Edwin
