I have only been collecting for 4 months and have 
about 20 cels (give or take) from different 
series.  The most cels I have is from Fushigi 
Yuugi, Jubei Chan, and J-Decker.

The one I would keep (if can only keep 3) would be 
:

Tasuki (FY)
Maskless Chichiri (FY)
Sesshoumasru (Inu Yasha)

Those would be the cels I would keep.  They also 
cost me my right arm, especially my new fluffy!  
^_^

J-Decker