Konis will offer the best ride qulity and keep the all important warrenty intact, expensive, non adjustable and will only give you the same ride height drop as the SS
Coilovers will offer adjustable height drops for a avarity of prices depending on brand you decide to go with.
Someone on here has already fitted Bilsten coillys but has posted pic's or a full review, another member on here has KW's varity3 which is fully adjustable damper settings aswell as ride height but are over £1300+