I'm using amorphous (thin film) panels. They're the least efficient per square foot, the least expensive, and probably the heaviest. Space and weight are not big issues for me, so I go with the "best price per watt."

There are so many big advances nearing production, and such an increase in production scale, that I'm not willing to buy more panels right now. Cost per watt is slated to drop substantially (that's the buzz anyway).