..it depends not just on who signs it, but on the 
setup of the cel itself.  On how aesthetically 
pleasing the autograph looks on the image.  I 
have more than once passed up getting creators 
autographs on a couple of my "primo" cels to get 
them on cels which I thought would look better 
with the autograph. I try never to get something 
autographed where the image is so large they 
would have to sign over the character.  
A prime example is my cel of Utena and Touga from 
the dance, where the signatures (needed space for 
two because I consider Ikuhara as much the 
creator as the manga artist Saito) fit 
wonderfully to either side of the two characters.

But this is of course just my opinion on the 
matter..