Depends on who you ask really, your going to get alot of different answers in here. At the moment though Linux and Mac are going through a bit of convergent evolution, with OSX using Darwin,and Linux becoming more and more desktop friendly, they may one day meet.
At the moment you can look at it two ways:
Mac is better learning curve, because you need to make less configuration choices, and the filesystem is designed to look more familiar, plus you can use some of the programs you already have on windows (office [BLAH], Photoshop, etc)
But you need to buy awhole new computer, that will cost you about 1 1/2 or 2 times as much as a new PC of the same qualifications.
Linux on the other hand will take you a little longer to learn, or no time at all depending on the type of Linux you choose. The programs are available, either the same program, or a substitute(ie Openoffice for MS Office), the best part is you can use your PC, or you can use that MAC you might have bought anyway, Linux works on both, as well as many other platforms. It's also Open Source, so if you choose a distro like Mandrake or Redhat you can download the entire OS for free, that also means that most of the programs are free as well, No $400 for MS office just open Openoffice after installing Manfrake or Redhat after installing, they both come with OpenOffice.
I recomend SuSE Linux Desktop
[ September 08, 2003: Message edited by: suselinux ]