I think that male collectors almost always collect only
cels of girls, but female collectors will do both male
and female.  I think the reason is that female collectors
dig the boys (mmm...tamahome...mmm...) but also think the
girls are cute or pretty.  For me, I collect hunky guys, 
but most of my cels are of sometimes terrifyingly strong
female characters I admire (and aspire to be?  ^_^)
Ryoko, Shayla, Nami, Yohko