This is a trick question. The answer in IT is always ... IT Depends.
There are several questions which must be asked. The answers determine the best OS (Operanting System).
How technically savy is the user?
Does the user want to pay a lot or nothing for their OS?
How user friendly does the user want the OS to be?
How powerful does the user want the OS to be?
What hardware is the OS going to run on?
......how much RAM?
......What type of drives, etc.
Does the user want to have to upgrade a lot?
What software does the user have to have work?
What software does the user want to have work?
What is a must have use for the machine?
What is a nice to have use for the machine?
So, in general my answer to your question would be:
For free and something to learn: Redhat
For compatibility and availablity of software: XP
For MAC, a MAC OS obviously.
Also, just saying "Unix" doesn't really mean anything. For true Unix, you'd have to have a server or a workstation - not a PC.
Under "Unix" there are many flavors such as Solaris, HPUX, AIX, etc.
Interesting you list a couple flavors of Linux but don't say "Linux".
Generally speaking, in business, if a user has a "workstation" it has more power, specialized hardware, over size monitor, etc. If the user is doing word processing and such - normal office apps - they have a PC.
I know one could argue that they have PC's that blow a workstation out of the water in memory, cpu, disk space, raw "speed" etc. It's more of a business IT term.
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