I suggest you save your time and money. I recently test drove a scion tc and was about to buy it when i looked into the honda civic Si. First, the scion is made very, very cheaply. i have three friends with the tc and all of them have broken exterior parts. mainly the trunk latch breaks soon after its purchased. the scion also has a bigger engine than the Si that puts out less horsepower and gets worse gas mileage. anyways, back to the point. i test drove a new civic si. it was love at first drive, more horsepower, better gas mileage (average of 29-30), a lot more fun to drive, and is made much better. plus Hondas are know to bea lott more reliable and are known to keep running past 200k miles. some might argue that you can put the TRD supercharger on the Tc and it will keep up with the Si. this is true, almost. after being supercharged the tc is barely able to keep up with a Stock Si. plus i read the reviews and the owners of Tc's say that the car starts to fall apart when you supercharge it, they haven't found one supercharged that lasted more than 15k miles. this is because of the supercharger design (it needs to be a "roots" design).
bottom line, go with the Si. better value, better gas mileage, better resale, and much better performance.