Butter or Lesser don't matter, usually people look for the most yellow in them (at least a trend I notice). I havn't seen anything where a darker/lighter lesser/butter makes a better BEL, I've seen a couple with some yellow but majority all seem to be the same clean pure white.

Just look for an animal you like, don't worry about the name attached to it. Do you buy a pastel because its a lemon pastel or because its a nice pastel regardless of the name? same thing with butter/lesser.