On the GTV V6 I've heard that the BMC CDA sounds great but actually lowers the power as the original filter is so massive it has a better flow rate than the CDA.
I quite like the look of the alfaholics replace element though, as big as the original be no oil to knacker the MAF. http://www.alfaholics.com/browse-parts-by-car/gtv-spider/engine-and-transmission/pipercross-performance-air-filter/