When I started I did a lot of books for just one artist (or writer for Stan). I considered them like single-signed baseballs. I tried to get examples of the work that I really liked in grades that I thought were reasonable (usually 8.0-9.4 for the Silver and Bronze books I was interested in).
I have also gotten many multi-signed books done as well, and for the hardcore SS crowd, I think it fair to say that more complete is more desirable. But it is not always a big deal. For example, I have ASM 123 single signed by John Romita. Gil Kane passed before SS existed, so he can't have ever been gotten. Gerry Conway wrote it and Dave Hunt worked on it. I don't think a Romita, Conway, Hunt would sell for much more than a Romita single SS.
But if you look at a Star Trek book for example, a book with the whole bridge crew will sell for tons more than just Shatner or just Koenig or whatever.
As with most things involving comics, it depends.