What year Scion tC is best?

One thing to be wary of when considering a used tC is that the car was marketed as being a “blank slate” prime for modifying and customizing. Scion sold numerouus engine and suspension accessories right along with the car, even including them in the car’s manual. The car and Scion’s marketing approach also spawned a huge aftermarket performance parts industry. Many were modified, not always properly. I’d avoid any that shows and signs of having been modified. It’s impossible to tell if it’s been done properly.