With one close exception, the SLK. It would come down to what your preference is between comfort and performance. If you choose performance buy the Porsche. The boxster and cayman are the same car except for the convertible on the boxster.

I loved the slk’s I’ve had. Just sold my most recent one last month. They are smooth and comfortable and the hardtop convertible is really great. The benefits of a hardtop when it comes to road noise but a true convertible for nice weather.