ASH is capable of much hotness - so I went for "I'd tap that". As far as the others go, I read a Spike/Willow once that wasn't as squickifying as I expected, but it wouldn't be my first choice. I love Ganya, I can easily read a well-done, believable Spike/Giles (although, only as a temporary thing, for some reason), I can easily get into Giles/Joyce, and if he wants Olivia, I'm fine with that. And then, there's Ethan...
Giles and Buffy just makes me shudder. I'd rather read Spawn, than Biles. That is not a positive statement - just in case that wasn't clear. :)