Well, I would chose eccentric. Not only because it's what I already am (lol), but I also think that, while my behaviour, which defines me for other people, would change, I would essentially stay the same person and still have an amount of control, while if I would chose insanity, it would be like giving up who I am to become a new person. Perhaps one that would act the same as before, but in the core a different one - a damaged one, even. I would lose control of my mind and that would be something I really don't need to happen to me.
I just noticed my arguementations suck.