The STI wing looks too over-the-top, even or a real STI. On a non-STI, you'd look like a poser with hideous taste.

The WRX wing looks good. It's also subtle enough to look good without looking like you're trying to impersonate a faster car.

If you get either one, ditch your third brake light in the rear window. Having both lights (spoiler and window) says "I was too lazy to switch over the wiring after installing my spoiler." Half-assed mods never make a car look better.