Personally I feel as though I'm the best mod on the site. I'll take your $250 bucks. Thanks!
FIRST MOD EVER SHOULD BE A FIRE EXTINGUISHER!
In all honesty, what do you want to do with your car? There is no best mod overall. If you want visual impact, I prefer the heritage grill or LED/SMD sidemarker lights.
If you want performance, Possibly look at Intakes or brake ducting from the ZL1. I believe it fits the SS and will allow a little bit more air to help cool your brakes.