It depends on what your looking for, what you use your car for and your budget to be honest.
The cup chassis is very capable on road and doesn't really need anything to handle better (imo), if your looking to lower it a little then H&R springs should give you a nice drop without ruining the ride (from other peoples experience). If your doing a good few track days then coilovers are probably where you should be looking to 'improve' the handling, but only if your happy to spend the cash and already feel your pushing beyond the capabilities of the standard suspension, which as I said is already very capable in the right hands.