Can't speak for Sedo, but in our experience one click typically works better if the term is very specific (like red tennis shoes). Two click often works better when more general (shoes) since a two-click lander lets the user further refine their interests.
That said, it's not a full-proof thing, it's best to test both if possible. Yahoo! (which we use at DDC) and Google also have restrictions on which domains can go one click. So sometimes there's just no choice in the matter.
Cyn