For home servers, CentOS 5 is probably the easiest to work with. (Don't go with 6. they removed a lot of the features that made 5 so easy to work with and just made 6 a general PITA. BTW, CentOS is just a debranded version of RedHat. So it was RedHat that made the bad design decisions.)
Windows Server 2008 R2 is the easiest to work with and has the most features, but it costs a bundle. I use it only because I got a free license from Microsoft's Dreamspark program. (That gives certain licenses to college students to encourage them to program in the way Microsoft prefers, but it is useful for IT students as well, since it includes licenses for Server OSes.