More often than not, I'm a pessimist - one of my philosophies in life is: optimism is the quickest & easiest way to disappointment. Having said that, there are occasions where I am optimistic - I can't think of any at the moment, but they do happen, just not a lot.
I think a general rule should be expect the worst but hope for the best - that way you can't be upset when whatever it is is bad, because you were prepared for it, but at the same time you can be pleased if whatever it is is good, because well... it turned out to be good.