I really don't knowif there can be a "best shot" 
in a series, but I do have a number of what I 
consider "perfect character" cels, where I feel I 
have the best possible cel of the character (not 
that there aren't other "perfect" cels of that 
character out there too ^^)  Some examples:


Gene from Outlaw Star




Nanami from Utena



Sakura from CCS



Actually, I've found that these "perfect 
character shots" seem to be the favorite cels in 
my collection... more than just important scenes, 
they capture the feel of the entire show for me ^^