When you compare any two cars, like the turbo Scion tC and the Honda Civic you have to start from big to small, working from unique parts of each car to more general items. For instance, the first feature to look at that the Scion tC can come with is the turbo package. If you get the turbo, it won't be much power added, but you will definitely tell a difference from the Civics lighter power, although the Civic Si is V-tech.
So what's better? Well, it all depends on your styles of tuning and the parts selection available for that car. Scion came out with a car that was basic and attractive, much like the Honda Civic always had been. However, when the turbo tC came out, they opened the doors to new auto tuners to come and purchase their way into another tuner car that has only just begun. This was attractive to many young kids who were always attracted to Honda Civics, and now are of age to purchase their own cars. The turbo Scion tC gave an easier route for people looking for Civics, simply because there are very limited sources on clean older Civics. Newer Civics have recently been sort of expensive and many daily working auto tuners want something cheaper, but still be able to customize.
If you are comparing the Honda Civic to the Scion tC, with respect to how many aftermarket parts and upgrades each car can have, I would have to say the Scion tC has out-ran the newer Civics. However, if you where to look at every generation of the Civic with respect to the numbers of Scion tC's, it would be obvious the Honda Civic tuner car industry is way deeper, larger, and older, having more recognition than that of the Scion tC.
