The ST2 and st3 come with a touchscreen radio with gps and a Sony sound system. The st1 has regular clothes seats, the ST2 has partial leather recaros, and the st3 has full leather recaros. I think all of the st3 models have a different center console as well. The cupholders are left and right, not up and down, and the hand brake is up a little higher. As far as the 13/14 and 15-17 differences are on the outside, there's some trim differences. Different bumpers, hood, and headlights are the only major appearance differences. Mechanically I believe only the major difference is in the late 14 and every year after they put a better rear motor mount in. I'm sure there's more, but that's basically what you'll be looking at.
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