I'm mostly a libertarian.
I used to be mostly a Democrat, but I've become both more cynical and more optimistic as I've grown older.
I'm cynical about the ability of Government to solve our problems. Most of the really big problems (wars, genocides, environmental destruction) are either the direct or indirect result of government.
I'm optimistic about people, though. Most people are good, and most of the really good things that happen in this world are the result of good people doing great things (how cool is penicillin? Or the Nature Conservancy? Or Wikipedia?).
I'm also optimistic about our future. Soothsayers have been predicting worldwide doom for thousands of years, but overall things are getting better all the time. We know more than our parents did, and learn from their mistakes, and we're getting better at remembering and learning and sharing.