I keep mine on the cool side because they dry out in just a few hours on the hot side. If I notice shed issues with a gecko, though, I do switching his/her humid hide to the hot side.
i put 2 moist hides in my terrarium. one on cool side and one on warm side. i have never seen them inside the cool moist hide, and they spend 8-12 hours on the warm moist hide
this varies depending on who you are. some people like it cold, other hot. this has been asked before. in the end it comes down to this.. hot side will theoritically keep it hot and humid.. but dry it out.. cool side will not try it out, but.. will it be as hot/humid as for long??