Actually, it's more likely the best, and owns the greatest market share of all available Unix products in the US. It could have been the same worldwide, if all your free foreign versions of Linux hadn't popped up as the new "official" operating system of every country who put in a language pack, stripped off Red Hat's name, and substituted "holy motherland operating system" on there instead.
Oh please. You have no clue what you are talking about. I am a hardcore UNIX admin with about 15 years experience. Name a version of UNIX and I have done it. Solaris, SunOS, IRIX, OSF1, Ultrix, NextStep, HPUX, AIX, FreeBSD, OpenBSD, Linux, etc.. If it has been used in the past 10 years, I have at least hands-on experience with it.
The decision to use an O/S has nothing to do with the cost of the O/S itself. The actual cost of the software is meaningless. Yes, if you are putting it on every desktop it becomes an issue, but when it is used on a server, it is a very small piece of the pie.
The major costs come from hardware and the people needed to run it. When picking a solution, if the company is smart, they will go with a solution that is not going to become some legacy O/S in a few years. They also need to take into account how difficult it will be to hire/train and retain people to run the systems. One of the main reasons Linux is so popular, aside from the fact that it works, is there are a lot of people out there who are familiar with it and there is almost no chance the O/S is going to go into the dustbin anytime soon.
I absolutely love Solaris, but can you guarantee it is going to be around in 5 years time? If you asked me that 5 years ago, I would be 100% sure it would be. Now, I don't know. My gut feeling is it will not be. (SUNW is currently trading at $4.17 a share.) Then what happens to everyone who is using it and has to transition to another platform?
I have worked in shops that have transitioned from Solaris to Linux. The cost of the O/S had absolutely nothing to do with it.
No. Mac OS X is the most widely distributed UNIX-based operating system. And it's the best operating system available anywhere.