I use a Mac, but I don't always use the Mac OS.
Some advantages of using a Mac:
Almost never will you fins something that doesn't work on its own. You can run a Mac having absolutely no idea what you're doing and still probably not have any problems.
Apple produces good hardware. Not just in the specs, but in the overall quality, they do outperform companies like Dell and HP, even on similarly-priced models. I've heard too many horror stories of friends' Dells, never heard of anyone running into problem with their Mac.
Most stuff will be compatible, and pretty easily so. It takes care of all the drivers for you (before I tried out other OS's, I didn't even know what a driver was)
OS X is very secure, and, unlike other computer manufacturers, it is only sold on machines that are powerful enough to run it extremely well. There is an excellent fit between hardware and software.
If you want, you can run Windows or Linux on your Mac. Apple produces good hardware, so even if you decide you don't like OS X you still have an excellent computer.
Cons:
Very restrictive, and not customizable at all. If you don't like the look of the Mac UI, too bad.
If something doesn't work out of the box, there is next to no way of making it work.
Vendor lock-in. Do you want to be dependent on Apple Computers?
Can be on the pricey side.
No gaming.
Fewer choices in configurations, meaning you may have to settle for a computer that has lower specs than you want or fork over more money than you want to spend for a computer that has higher specs than you need because there's no in-between model. (My MacBook is pretty good, but it has a crappy graphics card, so no gaming even when I boot up in Windows)
I like my Mac, personally, and OS X is a very good OS. If your concerns are security, stability, and ease of use, Apple wins.
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