I like to use calf body for flies size 18 and smaller, calf tail for flies larger than 16.

The calf body stacks better for the small ones and is a little easier to handle in small bunches.

The calf tail is much longer andhas more kinks, this provides a more bushy look for the bigger flies. One great tip I found was to use some anti-static spray (Cling-Free) on the calf tail, this makes it much easier to stack.