It depends on where im hunting.  If its somewhere I always get to hunt, I usally only pick up perfect teeth, and the larger teeth.  Now if I was say at the cliffs or lee creek, I would be picking up everything I saw, or at least until I got sick of picking up the little ones. 

It also depends on the type of tooth.  I find myself picking up every ptychodus tooth I come across no matter what the size is.  I have a thing for those.