Sedans: 03 is cost effective and looks more like a sport car with some luxury. However, not well refined. 06+ are beautiful, but expensive and a little more on the side of a luxury car and not as much a sport car (just depends on your preference really).
Coupe: Other than technical differences, bodies are mostly the same. So just go for the newest you can afford. I found 05's to be a nice balance between cost and age.
Above all, have fun with it. Pick the car you really love. I get excited every time I drive mine, that's why you're buying it afterall.
