What sounds like a better option for dormancy, the garage or the basement?

The garage is probably your best bet provided that it has a window that will allow light in. Most garages are unheated, but seldom get below freezing. If your basement has a window, and it is also unheated, this would be a fine option as well. As you can see it depends on which place gets the right amount of light and has the right temperature.

Choose the option that provides the most sunlight with the temperature in the 32 to 65 degree Fahrenheit range.