I just used the vehicle configurator from costco.com and it has only QuickSilver Plus material and says this...
QuicksilverPlus is an excellent choice for sunny climates. The silver reflective layer reflects sunlight and U.V. rays, yet is very water resistant.
I don't know if this is the best for our winters.
Are you planning on storing it outside or in a garage? I picked up a cover at
http://princessauto.com for $25.00 and it works great. It may not look that pretty, but under snow who cares.
I am not going to store the car, I plan to drive it this winter, with winter tires.
EspressoBoy