If I can afford one good cable, which component?

In my experience, putting the best power cord on preamp or integrated is the way to go. Not on the source, not on the power amp. And the rest of the cables, yeah, follow the signal. However, as Elizabeth said, it might be different in different set-ups even if only to a certain degree. Current from the wall and regenerators/conditioners is another subject.

Also, the high-end fuses are worth the money. Get the power right first and then experiment with cables.

i noticed the biggest improvements upgrading the pc's on my digital source (dac and transport). 2nd place was my amp. i agree with others regarding upgrading the outlet as well.

the fuse upgrade thing is interesting as i just ordered a pair of supreme hi-fi fuses a few days ago. should have them soon and look forward to finding out for myself. again...i'll be starting by upgrading the fuses in my source dac.... and go from there.

The signal coming from the phono stage is the most delicate. If your arm doesn't have a dedicated wire...ie: cart pins to phono stage in, I would pay most attention to that cable first.