Any of the BSD flavors would be better, in my opinion. Of course, there is a lot of hype surrounding Linux right now, especially since it is number 2 in server shipments. And there is also tons of documentation and people to help you out with setting up Linux.
I have yet to find any companies that offer BSD classes, but there are more and more that are offering Linux classes. If anyone knows of companies that are offering BSD classes, please let me know.
I will recommend BSD, but be prepared to do some serious learning. Even installation is not simple.