You're the only one that can decide, but I would drive all three cars like Brucelee said before making a decision. If you're after a lot of HP and straight line speed don't get a Porsche, but if you want something that can out handle just about anything look at the Boxster and Cayman. Personally, I would choose the Boxster because you have the ability to have a hardtop or a softtop, but it all really depends on what you want.
Also, the maintenance isn't too bad. You can DIY just about everything on this car if you want, and unless you have a major problem the average maintenance price is about the same as any other german car.
Good Luck with the Decision!
