I got UUC SwayBarbarian. It's definitely the best mod for its price.
u can feel the car's very under control in corners even at high speed. You can also fine-tune the car's handling characteristic, ie. dailing in more understeer or oversteer. The front's 25.4mm and the rear's 23.8mm. The RD set has a thicker front but a thinner rear, which keeps the stock understeering nature while the UUC one is designed to neutralize the car's handling characteristic.
For more info: http://www.uucmotorwerks.com/html_pr..._bar/about.htm