Where and on what sort of roads will you be driving the car? You need a very challenging road or a track to get to the Porsche's sweet spot. In typical daily driving they can almost be boring, they're operating so far below their potential and provide so little sensation while doing so. The new turbo engines might make a difference here. Or not. In ways I preferred earlier generations of the cars, which were more compact and less insulated.
The Corvette is more fun in typical daily driving, but also needs a hell of a road (or a track) to really enjoy it. Its capabilities are just so extreme. For outright bang-for-the-buck it's not possible to beat the Corvette, except possibly with the new Camaro. I'm testing one early next month. I can already report that the windows are ridiculously small.
I like the latest Cadillacs, especially in V form, but they don't approach true sports cars in driving fun. Same goes for something like a BMW 4 Series. Just too big, heavy, a refined. I enjoyed the 2009-2013 CTS-V more than any of the current crop, as it was more raw. Also very thirsty.
The new M2 is the best bet among current BMWs.
I greately enjoyed driving the previous generation Audi TT RS. A very fun car even in typical daily driving. But the next TT RS is about a year away, and it remains to be seen if it will be as fun as the previous one.
Refinement doesn't get in the way with the Alfa Romeo 4C, but most people consider them too uncomfortable and too impractical. I haven't spent enough time driving one to provide an evaluation. Before spending $65k you might as well play the field and have a fun test drive. Maybe you'll find you really like it.
Finally, if you don't mind saving a lot of money it's hard to have more fun on 90-plus-percent of public roads than in a Mazda Miata.