Strangely enough I had both these cars in mind a few years ago. Eventually it came down to a choice between a Boxster/Cayman for back roads fun or an E Class Convertible for European touring & as my daily. The Merc dealership where I ended up had both a Boxster & E convertible in stock & I decided that the E met my requirements better having driven both. However I still needed a car for back roads fun & that led to buying the Clio a couple of years later in addition to the Merc. I still have the Cayman itch to scratch though. In your position, assuming that the daily/family car is covered in the Shulver household that's the route I would be taking. You can have an ordinary, very capable, hot hatch in the Fiesta, or something truly special that all petrolheads would appreciate.