Best for who? 90% of the market has no interest in building an operating system from the ground up. Linux is great if you are technically sound. Linux is NOT best for most computer users who want a desktop that lets them surf the web, watch videos, listen to music, et cetera out of the box. Lets be honest, but Linux is a hassle. Yes it's got a lot more functions available, but how often do you really need to know what your CPU usage is?
There just isn't 1 thing that Linux offers that my Windows 7 PC can't do that I would WANT to do. And as far as security and stability goes, never had my box crash or hacked. Most Microsoft bashing is unfounded, and seems to be done out of the coolness of hating Microsoft and being in the "know" about Linux. I have messed up some settings in Linux before and messed my settings up. I've had compatibility problems.
I'm not running a server. I'm not some uber programmer or elite black hat hacker. Not to mention most programs and support are geared towards Microsoft. Everything is simply more difficult in Linux. Can't think of anything that's easier that makes Windows worth it to me. It's just the sad facts.
Don't confuse me with saying that Linux doesn't have it's uses. Put a linux distro next to Windows, and 90% of America is going to look at you and ask "Why should I bother?"