This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
As far as I am aware there is no longer a standard Unix, just flavours of Unix. Google will find you a host of Unix flavours. Take your pick of those that will install on your hardware. I like the Ubuntu implementation of the Linux flavour but the Fedora implementations are pretty good. I have used FreeBSD, Solaris, OS X, GNU Linux and other. The differences between them and my concept of Unix are sometime quite large (OS X for instance is pretty but very different) but all support the standard Unix utilities including the shell (sh).
Retired horse trader.
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There never was a standard version of Unix. Unless you want to mean "pick one" (such as SVR5).
Technically, there's no standard version of Linux, either, but the differences are mostly cosmetic in Linux, whereas the differences between Unixes were often pretty fundamental. It's one of the reasons why Unix didn't already own the world when Linux came along.
Some Unix distros come with their associated hardware, such as AIX. Others are more portable, such as OpenSolaris and the BSDs. At the moment, Oracle is being troublesome and the open Solaris community is regrouping, so one of the BSDs would probably be your best bet.
Customer surveys are for companies who didn't pay proper attention to begin with.