Sure, I think that choosing from only optimism and pessimism it is best to be a pessimist. Optimists can occasionally be blinded by their optimism and be totally ignorant to certain things. If you ONLY focus on the positive you block out the negative and become more susceptible to getting screwed over in society. Optimism is a shaky road because it is tangled with new age crap that leads to "blinding optimism" in which people simply don't focus on bad things.
Pessimists can more easily accept the negative parts of life and can then get over them. This repetition of focus on the negative will allow them to better evaluate them. They will then come to the realization that suffering and bad things are inevitable and that they can overcome them. Pessimism also makes better critical thinkers because they will always be mindful of the bad and potential ways their plans can fail so they have the knowledge to prepare for more.
A new study came out which shows that pessimists have better health than optimists and prepare for more potential problems with their health because they know that things can always go wrong. Meaning pessimists live longer.
**Note** All of these paragraphs are coming from the assumption that I may only choose pessimism or optimism without any middle ground or implications.