Well, the Toyota Prius is the hybrid that has been on the market the longest (first hybrid available in 1997), and since current US sales put it at around 50% of all hybrids sold, I would have to say that Toyota would be the most likely branded hybrid that someone would have (especially when adding in the Highlander Hybrid and the Camry Hybrid, and the Crown hybrid, Estima hybrid, and Alphard hybrids as well... would you also add in the RX, GS, and LS Lexus hybrids too?)
I currently own a 2001 Toyota Prius. My husband used to also have a 2004 Toyota Prius, but we sold it when we moved to where public transportation is far easier/cheaper.
www.hybridcars.com