Why the Amstrad CPC was best in the 'general 80s 8-bit computing' category, in my opinion:
* It came with a monitor - no need to hog the family TV
* Graphics were decent, especially static images, some categories of games were excellent, but high memory requirement and lack of smooth scrolling held back many cross-platform titles
* Good range of business software because of CP/M and 80 column mode
* Also productivity software - you could reasonably do your homework on the machine with Amsword/Tasword II/Mini Office 2
* Excellent value for a CP/M machine
* Decent amount of RAM, expansion options
* Late 80s it came with a TV Tuner box, solving the teenager's bedroom needs
Runner Up: Commodore 128
Best Gaming 8-bitter: Commodore 64 - SID, Hardware scrolling and sprites, massive market meant lots of titles, and it came out 2 years before the CPC. Terrible disk interface.
Oddly enough it had some decent business/productivity software due to the market size, but the lack of 80 columns and low contrast interfaces was a negative.
Also Best Audio because of SID, apart from some boutique systems (Apple IIGS for example).
Best Value 8-bitter: Sinclair/Amstrad Spectrum Range
But graphics could be terrible unless skilfully designed, where detail, designing for the hardware, and good use of splash colour could be a nice benefit. Palette very garish - C64 hi-res attribute mode could look a lot nicer.
Best Business 8-bitter: Amstrad PCW by a mile - it redefined the marketplace. Apple II does need to be mentioned here, because it was a lot earlier, and Visicalc created the spreadsheet. The Apple II would win if I was thinking from a US perspective.
The Atari 8-bitters were strong machines, although the games tended to rarely utilise the hardware to the full, meaning they looked bland. Often 4-colour in MODE 0 aspect ratio with some sprites. They were also costly. Atari 130XE was the pinnacle.
MSX1 was a worldwide system, but had many of the Spectrum's issues but with a TI graphics chip that at least had sprites. Coarser scrolling than the CPC! Many solid games due to Japanese involvement, but not a massive hit in the UK. Some systems were quite unique though - some with synths, some with laser discs... maybe I can award it Best International System or something, although C64 is a strong competitor.
Best Educational System: BBC Micro by far, but the RM Link 380/480 systems were strong early on too. Costly though.
What else sold in the millions?
Much as I love the CPC+, it's too niche, and too late, to be a fair addition, and lack of software rules it out.
Ditto for the Sam Coupe, Z88, etc.
Enterprise 64 had strong hardware, but the sales failed (launched too late). Unique design though, but cursors would have been better in the end. Maybe if they'd used a 6MHz Z80...