Nuclear. It allows for waste to be contained easily (double steam systems release almost no radiation into the environment), and with a long term storage facility like the one proposed for Yucca Mountain, we can easily use nuclear power for hundreds of years.

That said, I also think that wind and solar are good things to pursue. Once solar gets down to the 'pays for itself in 5 years' level, I think it will become very widespread. Especially if a diesel hybrid semi truck hits. At that point, our major transportation fuel consumption will be airplanes, and we might be able to do a hydrogen fueled plane.