I found MIPS (R3000), SPARC, and MC68k about the right size for an ISA. Things like PIC (and similar microcontrollers) and older 8bit CPU like the 6502 and Z80 always felt a little limiting to me. I think those (MIPS etc.) were also a great point for higher-level (C, etc.) languages to be useful/interesting.

I guess each to their own though.