Anyway, not sure I actually did my round up, so here goes.
Liked the Z80 as this was the first CPU I actually wrote anything for. Pretty big instruction set for an 8-bit processor too and a fair few undocumented instructions.
Never really did much on the 6502. Appreciated the design though, where the Z80 took at least four clocks (and potentially a lot more) to do anything at all, the 6502 was pretty much hardwired in comparison and had a much more uniform execution speed. Unlike the z80 the machine was register sparse but the zero page made up for that. In those days, accessing memory or an internal register made very little difference speed wise.
Loved the 68000; from an assembler programmer's perspective it was almost the perfect design. Each major revision brought something to the table beyond extra speed. The 68020 was even more fun to code on, you learned a bit more about pipelining your code and how to leverage an instruction cache (tiny as it is). The 68030 introduced a datacache that was equally tiny but also fun to try and use. The 68040, for me, was almost a perfect CPU by then. Shame about the heat but having everything on chip and a performance that laughed at the 68030 more than made up for that. Caches were finally big enough to be really useful and the move16 operation made a difference when shoving data to chip ram.
The 68060 was a lot more challenging to code for, since you finally had to take superscalar execution into account to get the best performance. Alas, this is one M68K I don't currently have
x86
Everything prior to the 386 was a complete joke and unworthy of mentioning. The 80386 wasn't bad though, once you got out of real mode and into flat memory space. From an assember coding perspective though, the instruction set remained a bit of a dog's dinner. The 80486 was better again and finally started to reach (at the time) silly clock speeds. One thing they had that I wished the 68000 had was the bswp instruction. Having to use three instructions on the 680x0 to byteswap one longword seemed very odd, given that it's not an uncommon thing to have to do. The pentium mmx introduced SIMD but I never really did anything x86 since.
Contrary to many folks here, I rather liked the PPC. The 603e on my Blizzard was a whole new toy and one that had a programming model that was quite fun. It's probably the only RISC architecutre I can say that about (save ARM, which has some cool features too). Writing effective code for WarpOS was (and is) quite a challenge in it's own right. Architecturally, 32 GPR registers are a lot of fun from an assembler programmer's point of view, as are 3 operand instructions. I also like the fact that you can basically decide which arithmetic/logic operations should update the condition codes, since this allows you to tweak loops and the like in a way that was much harder on 68K. Actual syntax, not so nice. Bit ordering seems bizarre if you are used to M68K, since bit 0 is the MSB and bit 31 the LSB. Never really understood the purpose of that.
Never did get into PPC beyond that. I have a G4 machine that I need to get into coding. Particularly interested in the altivec stuff. The permute features in there seem rather nice and a bit unique maybe.
x64: Well, this was a surprise. An x86 derivative that is actually fun to code for. The 16 register model is a nice compromise IMO. I'm still learning it though, so Jury's out.
ARM: Quirky but cool. Especially liked the conditional execution of instruction feature, far more effective than having to branch somewhere just to execute a single instruction.
MIPS: never really got into this, so can't say.
Alpha: Did some computational chemistry coding on this beast. It was all in C though, however the compiler had vector extensions for the chip. Once you figured out how to use them the speed increases for all that n-body charge force calculation could be sped up nicely. Alas, since then, GPU coding has shown where the real future for that sort of computation lies.
With the exception of the 8086/186/286 it's probably fair to say I like most CPU's
It's hard to hate any, they all have their character.
