I don't have a Mac OS X so i just can report from friends of mine.
Most of them with Mac use MAMP and are very happy with it.
XAMPP for Mac OS X has one big problem: there is no active XAMPP Developer for that environment, so XAMPP development for Mac is paused at the moment and getting support for that environment is more difficult that for Windows, Linux or Solaris.
There is another big player for MAC: Zend Server (CE) for Mac OS X
. Maybe you want to try it out and tell me how much you like it