If you're just starting out exploring these options, I would recommend Linux first. Linux will allow you to have a nice looking GUI, with most of the command line options available in UNIX. Since Linux is based off of UNIX, many commands are the same- although there are many different commands as well, even in the different flavors of Linux. It really comes down to what you need it for. I can't think of any advantage UNIX has over Linux off the top of my head. No matter what you are planning, Linux is a good way to go.