As much as I love the looks of the Alfa, and the raw character of the car is very appealing, I'd go Cayman, unless a test drive convinced me otherwise. From what I've read/watched, the Alfa suffers horribly on anything other than billiard-table smooth surfaces. Also, I know that the two pedal flappy paddle transmissions can be awesome, but I'm on old curmudgeon that would want a DIY shifter, which thankfully, Porsche still offers.
The lack of dealer support and infrastructure for the Alfa is also concerning, and given how temperamental cars in this class can be (Germans and Italians?) that might end up being a very big deal. Not only is there a lot of Porsche dealers, there are many excellent indie shops out there.