I'd settle for this:
- System-wise (OS/programming) all Amigas ever were 32 bit; hence the Amiga is a '32 bit system'
- Performance wise A1000, A500/2000, CDTV were 16 bit, due to their 'undersized' data bus. A3000, A4000/1200, CD32 were 32 bit in all regards (well the 1200's EC020 has a slightly downgraded address bus, but that doesn't have much impact in performance).
This does match the Megadrive as 16 bit as it didn't have much of a system and only performance mattered.
btw: that's why Atari labeled their machines Sixteen/Thirtytwo -> ST, later came the Thirtytwo/Thirtytwo -> TT. ;-)
