Well I know that "sticks like sh*t" does seem to stick things quite well.
The other one, I've never tried.
But when I was a boy, the expression my dad always used was "sticks like sh*t to a blanket"
Now one can imagine, with a blanket being all fluffy, that sh*t may indeed stick quite well to it.
When someon'e done scientific test on the matter, do come and tell us the results, with pictures :coat