Easiest for me is curvy female characters and muscular male characters because I like
to draw in an exaggerated style.
Drawing obese characters is probably harder when you 1) haven´t done it often 2) try
to draw them realistically. But that´s just a matter of practice and knowing where the
body fat has to be but that´s the same with muscular bodies, you first have to know
about the muscles, observe, have reference etc.
Hardest to draw for me are kids because I never draw kids. Pretty much like @simplykit wrote.
I don´t find hands hard to draw at all after I have been practicing it for a while, there are only
a few hand poses which are hard to draw for me (fists mostlly)