From my experience with my two current cats, females are sweeter. Nicodemus (female) is really sweet and cuddles with me every time I sit down (and looks happy and content and purrs wether I pet her or not) and sleeps with me every night. Tobias (male) on the other hand, most of the time keeps to himself and only on the very rare occasion will come and cuddle with me (generally only when he's cold after I've given him a bath). So I'd have to say that females are definately sweeter.
Also, my family have owned quite a few cats and it's been the females who have been consistenly the sweeter cat.
Randi