which anti roll bar do i upgrade to?

I've got Neuspeed 19mm rear and 22mm front from AwesomeGTi, corners way flatter than before (and less jiggly over bumpy roads too).
 
Sorry for silly question but what does the anti roll bar do and what's the advantages of an upgraded one? I'm not too much of a tech person you see lol :)
 
Anti roll bar, its all in the name to be fair. Its a BAR, thats connected to both wishbones at either end, with it being fixed to the subframe that assists in stopping the natural ROLL of the car when cornering, hence an ANTI device. Upgrading means fitting a bigger bar with more torsional rigidity, hence stronger which means less roll. The rear S3 ARB is laughable, its like a toothpick!!
 
I think R23 ARB's are a pretty common upgrade arent they on the S3 without breaking the bank?

I've got KW ones on my A3 and think they're great.