To me, being nice is the 'easy way out'. I'm much more likely to get what I want when I'm nice, and people in general seem to like me more. In fact, being nice makes things so easy that in the past it seemed to be too easy, too boring.
However, when not being nice, I have to be mean, which ultimately is depressing unless I do some sort of complex logical acrobatics that never quite make sense enough to actually work, and I always end up feeling bad/depressed/etc.
There is a third technique though, and that is limiting interaction to the bare minimum. When I feel I must interact, I am generally nice. That said (written), I'm still not always in complete control of my raw emotions, but I'm much better than I was - for instance, I actually have a concept of not 'having to do' what my emotional center wants me to do
An odd thing about being mean too, if you 'hide'/express your meanness as humor, people will often go along with it, even thinking it makes you a 'fun person'. It's still being mean, though. And if nothing else, mocking others always made me self-conscious that others would mock me back, whereas when being nice, there is no such worry - so even from a selfish standpoint, it reduces general fear to be nice rather than mean/comedic.
Oh, technically you could also use self-effacing type humor, but I never understood that at all. At best it's a way of apologizing for a mistake. Usually though it just makes the self-effacer look like an idiot (which I guess is the goal after all.. odd).