UNIX or UNIX like operating system offers many flavors. Most Microsoft users are stuck with Windows NT / 2003 only. However, UNIX users can select a variety of UNIX like oses:
+ Linux ( Red Hat / Debian / Suse and other distros)
+ Solaris / OpenSolaris
+ BSD (FreeBSD / OpenBSD / NetBSD) etc
Few years back I used work at largest ISP in India and our team used to mange an average 8 operating systems to support our enterprise grade customers. It was headache for me as I had to document, patch and monitor each operating system. These days I recommend selecting one operating system, which may result into saving time and money. But, how do you select perfect UNIX operating system for your business? You should always consider following factors while selecting UNIX like oses:
Ease of use - Must be easy to use.
Reliability & Stability - OS must be stable to run your business and should work under heavy loads.
Budget - No one has unlimited budget or luxury to select fancy stuff. Evaluate pricing based upon your own IT budget.
Hardware / driver support - Does UNIX hardware vendor offer good support?
Application support - Does it run Oracle or ERP software? Make sure all software compatible with os.
Vendor support - Does UNIX vendor offer good support? Does that includes phone support or email support or onsite support?
Security features - Look for security features and past security track record
Addon features - Look for bundled features such as backup utility or special software. Can you modify kernel? Can filesystem hold millions of tiny files and so on.
Expertise - How much experience and expertise you have on staff to manage OS.
Scalability - Will OS scale with your business? How does OS scale when the business grows? Watch out for clustering and HA support.
OS market share - Find out if OS dominates market. A massive user base means good support and lots of skilled workers.
Community support - The best support can come from newsgroup, forums or mailing list.
Patch management - Are patches available immediately? Find out more about security disclosure policy.
Staff training and certification support.
If in doubt, ask other people or admins - Talk to your users and find their requirements. Ask to other admins or people about the requirements rather than vendor. People using UNIX oses for a long time have practical knowledge of many things and they may able to provide guideline.