you could have both operating systems if you wanted.
free (as in beer). doesn't cost hundreds of dollars like windows.
open source community - most programs are released as source code, and therefore free.
generally more stable than windows. (longer uptimes)
large variety and amount of programs/projects, which means plenty of freedom of choice. (for example, instead of being locked into one window manager, you can choose between Gnome, KDE, fluxbox, openbox, blackbox, icewm, afterstep, enlightenment, windowmaker, xpde, xfce, ratpoison, waimea, fvwm, evilwm, etc - you get the idea.)
a lot more modular - linux is essentially just the kernel, or core, of the os. all the other components are separate programs written by many different people. while it can be a little daunting to see so many different names, it also allows for flexibility. for example, you could completely omit the xfree graphics server if you didn't want to use a graphical gui at all, and you would get some extra free space. it makes sense on a 386, for example, which probably would have a hard time handling a graphics server. plus, i bet with a 386, you'd need all the space you could get.
more of a 'tweaker's' os, as i call it - if, for example, experimenting with various compiler flags to get the best optimization and performance out of your binaries is your thing.
not nearly as popular as windows. which means that all those virus writers and script kiddies go after windows, the os that everyone uses. i think linux has had a number of viruses in the single digits, or something low like that. however, the lack of popularity can also be a bad thing...
not nearly as popular as windows. which means very few commercial games and apps make it to linux. it's definitely not for playing the latest games, using photoshop and 3d studio max, etc. there are... 'equivalent' projects of sorts, but they are usually not as good/advanced.
steep learning curve. although user-friendly distros like mandrake make it relatively easy to do a lot through a gui, it still is a bit more difficult to get into. and i'll bet it's extremely difficult to get into using the command line if you've never used a command-line based os before.
see this thread for an example:http://forums.gentoo.org/viewtopic.php?t=42347
not many... safeguards against user error. if you rm * and delete everything in an important directory, you're not getting any of it back. although some of the window managers have their own kinds of 'recycling bins,' i think.
along the lines of 'not very popular,' linux is not very supported at all - you'll have trouble if you're the kind of person who calls tech support. if you call your isp to get help, and mention that you use linux, well... good luck getting that support.
i'm sure there are many more points to be made, but these are the only ones i could think of off of the top of my head. perhaps someone else could elaborate a little more.
i can't really give you much of a for/against recommendation without more info on your computing background, and more importantly, what you do on your comp and what you want to get out of it.