Big question is going to be how much you are looking to spend.
My car was geared towards more of improving handling and eliminating some of the issues with the rear axle. So I replaced the stock struts and shocks with some Steeda's, camber plates, 1" lowering springs, Whiteline Watts Link, upgraded LCAs and relocation brackets, Steeda X-brace, and Boss rear sway bar.
The car feels completely different, I love it.
2011 V6 Mustang - Premium 202A Spec (Pony Package) - SOLD!
2014 V8 Mustang - Premium 400A Spec
6 Speed Manual, 3.31 Rear
Black, Charcoal Black
Comfort Package, Security System