REALZEUS has a point about the cost of ownership, Ferrari's can be potentially crippling. As for the fun stakes, depends on what turns you on. Having had the privilege of driving both and owning a Porsche for a couple of years, I personally would opt for the Carrera. It is definitely a heart and head purchase, as opposed to a heart purchase that the Ferrari would be.
Ultimately though, if you've got the money for either one plus the running costs, then buy the car you desire. I'm not sure there is a wrong answer.
Another option worth considering is forget buying the car, take out a membership of one of the many super car clubs. All the pleasure and none of the hastle.