The 6809 was almost certainly the ultimate 8-bit processor design since it had many 16-bit features as well as advanced addressing modes, stack handling and advanced instructions including a multiply.
The crown of "Best 8-Bit CPU" should probably go to the little known 6309 CPU, an advanced variant of the 6809 made by Hitachi under license from Motorola (https://en.wikipedia.org/wiki/Hitachi_6309). It booted up fully compatible with the 6809 but could be switched to a 'native mode' where it would execute 6809 instructions 30% faster, have more registers added and a significant number of additional instructions including divide. Being fabbed in CMOS, it could also be clocked much higher than the 6809's 2 Mhz, up to 3.58 Mhz.
Anyone wanting to create "The Ultimate 8-Bit Microcomputer" from early 80s components would want to start with a 6309 as the CPU and perhaps marry it to the 9958 video display processor used in 8-bit MSX2 computers which was probably the most advanced VDP of the era since the 6847 VDP Motorola designed for the 6809 was extremely basic with no sprites or extended palette features. For sound the best 8-bit era chip would be one of the Yamaha FM chips commonly used in MSX2 machines. Unfortunately, no manufacturer ever married these components into a world-beating Ultimate 8-Bit. It would have been an amazing machine for the time and certainly held the position as top hobbyist lust-bait - at least until the arrival of the 68000-based Amiga.
The crown of "Best 8-Bit CPU" should probably go to the little known 6309 CPU, an advanced variant of the 6809 made by Hitachi under license from Motorola (https://en.wikipedia.org/wiki/Hitachi_6309). It booted up fully compatible with the 6809 but could be switched to a 'native mode' where it would execute 6809 instructions 30% faster, have more registers added and a significant number of additional instructions including divide. Being fabbed in CMOS, it could also be clocked much higher than the 6809's 2 Mhz, up to 3.58 Mhz.
Anyone wanting to create "The Ultimate 8-Bit Microcomputer" from early 80s components would want to start with a 6309 as the CPU and perhaps marry it to the 9958 video display processor used in 8-bit MSX2 computers which was probably the most advanced VDP of the era since the 6847 VDP Motorola designed for the 6809 was extremely basic with no sprites or extended palette features. For sound the best 8-bit era chip would be one of the Yamaha FM chips commonly used in MSX2 machines. Unfortunately, no manufacturer ever married these components into a world-beating Ultimate 8-Bit. It would have been an amazing machine for the time and certainly held the position as top hobbyist lust-bait - at least until the arrival of the 68000-based Amiga.