You can't go wrong with any of them, OEM rims are nice for what they are, but aftermarket rims makes your car more "unique".
I personally don't like the design of the Ultraleggera, had the choice between that and the Leggera HLT, and I took the Leggera HLT... looks way better in IMO, despite the fact that the Ultraleggera's are lighter.
Also stock rims weight approx. 28 pounds, lighter 18" wheels weight approx. between 16-18 pounds which is big difference on unsprung weight