What is the quickest VISA to gain entry into the US? Fiance, tourist, work, etc...?

I have met the most awesome woman. Only problem is that she lives in Colombia, and I live in Los Angeles. I just got back from visiting her, and would like to see her here over the Holidays, or as soon as possible thereafter. She thinks a fiance visa is the quickest, but as I understand it, you HAVE to get married within 6 months, and if not, then what? I also understand that some visa's take forever to be granted, and they are only temporary. Does anyone know what would be the quickest visa?