Among the pessimistic category I've met people who take on adversity with confidence and those who wither in its face. The first are mostly successful teachers, leaders, workers and artists, the latter often lead a simple life, sometimes with dissatisfaction. I can imagine there are other variables that will stop me from claiming one way of living as better than the others. Although I personally can't stand being around optimistic people for too long. I'm not sure what my team is but most of my friends would probably classify me as realist.

Even though optimistic people are prone to being hit by reality, they seem to always bounce back and easily find joy in things others wouldn't. I don't know what the connection is but I'm confident there is one.

I think most people would defend their "ideology" when confronted with this question. I can certainly think of situations in which being more optimistic would benefit me, but I wouldn't want to become one because my modus operandi has benefitted me just as often. As for "big situations", a pessimist might fare better and therefore be happier when it counts, but an optimist can argue that they're generally happier in their day-to-day life. Even if the pessimist strikes the life changing job opportunity, they'll spend their working days concerned and cautious. I know 80+ year old people who are frugal, skeptical and pessimistic. At this point I can't help but believe it's intrinsic to their nature.
I do agree that one should try to be versatile in their way of thinking depending in the situation. Learning to make those decisions is a problem in itself.