 I had driven 3 straight MB Cabs and no longer needed a back seat; I wanted a roadster since a teen. I think it was the Alfa Duetto Spider 1600 from one of my favorite movies, The Graduate. The latest Alfa, Jag and FIAT were eliminated as perceived as unreliable. The R8 way too pricey , the SL  drove too "boulevard like" ie not sports car like. The SLK and Miata were, forgive the term, chick cars; the Nissan 370 and Corvette, again, forgive, red neckish.  That left the Boxter S and the Z4 35IS. I drove all of the above and though the Boxter S was great, the Z4 35IS REALLY stood out; I would describe driving it as a "Tight Glove-like fitting, Rocket". It doesn't hurt that I love the lines and don't see one everyday, as I do Boxters. BMW reliability as well as the 5 Year 100K  extended warranty that came with the car didn't hurt either.