The 68k (and it's 8-bit semi-cousin, the 6809) were very nice. However, unlike the Z80, the 6502, and x86, they're no longer being made, and are increasingly rare.
They're in the "legacy" line and labelled "not recommended for new design" but I think that's just design opinion and doesn't imply it's no longer made.
I'm sure this video has done the HN rounds before. It's a slow but fascinating watch. "Motorola 68000 Oral History Panel" from original Motorola team members. https://www.youtube.com/watch?v=UaHtGf4aRLs
68k Macs are easy enough to find on eBay. Grab one of the old Powerbook 1xx series laptops and you have a self-contained development station that's less expensive than many modern microcontroller dev kits.
The Z80 only has a 16-bit address space.
My favorite CISC architecture is the 68000 series.