What are some of the most popular versions of Unix and why?
It depends on what you want to use Unix for...
There's alot of posts on here about the same thing:
There was also a poll awhile back that's in the FAQs now...
Basically, your question is very broad. I can't speak for others on here, but personally I enjoy a question that's more specific so it can be answered more specifically. A problem with an actual answer. These types of posts can potentially end up in flame wars with people saying which type they like best. I'd guess there's polling sites out there on the 'net where you can find out which flavors tend to be more popular though, so that may be a place to start. Also, research each operating system ... the most "popular" one may not even be useful to you.
i think for each manufacturer is his own UNIX the best... you have to look to the homepages to know why they think so...
the most widespread UNIX derivat is sun solaris (www.sun.com)
I've got a nice URL for all known LINUX distris
hope it helps
bye bye Pre�y