It's such a funny question, as obviously it's everyone's ultimate desire to be happy! Riches are only desirable because they buy the means to happiness. Happiness is the desired goal. So the answer (happiness) should be obvious.. but interestingly it isn't. Most people say they'd prefer to be rich.
I heard an interview with Paul Mckenna, the hypnotist, about his books on losing weight. He asked many many overweight people why they wanted to be slimmer. "To be happy" they all said. So he wrote his book about how to lose weight successfully, and initially titled it I Can Make You Happy. No one was interested, it was a flop. He retitled it and sales skyrocketed. It was now called I Can Make You Thin.
Strange isn't it!