What a subject, and one subject to heated debate on both sides. but lets forget who started there photocopiers first and look at what makes Mac OS X better than Windows and more specifically Vista.
So both OSes are good at what they are meant to do;manage hardware resources, its all a OS has to do and they both do it well, but on-top of that there's the nice pretty glass(aero/aqua if you prefer) on-top and then the applications themselves, the stuff we all use.
So Windows has VB and its various implementations of C for your coding no real clear cut way of making a program for people like me (beginner) but VB is extremely simple to get your foot through the door. So what about Mac OSX while theres Automator & Applescript and there's Xcode and all that encompasses: cocoa and carbon. This is what makes the Mac much better from a users perspective and quite possibly a developers perspective also, there's a clearly defined way to code and make the program, Apple has created extensive frameworks to code for and into, theres no complicated way of making your own chances are there already in the OS. An example of this would be creating a zip, typically on windows you would get winzip and zip up the file, with Mac OSX and Quicksilver a few key presses launch up the framework and compress the file to whatever you want.
So what makes it better, the simplicity of making extensible programs without the program being sick with DLLs and files on the Hard Disk, only one OS gives this seamlessly without hassle and you guessed it's the Mac.