Pierre - it IS a sheep shank. The name I believe comes from it having the two loops present, which used to be used to tie the legs of a sheep for various purposes, but which can then be shaken out once the animal is released.
As for my favourite knot, it has to be the adjustable grip hitch, but tied with a slipped end so that the knot can be undone easily. This is what I use on hammocks, tarps and guylines and it makes adjusting tension on them a breeze. Its also very quick to tie, makes a simple loop, and can be tied fairly easily with one hand with a bit of practice.