try freebsd. it will piss you off the first few times you install it. and confuse you. but once you learn the software installation procedure's it will make you very happy.
as for the differences between distros, most have to do with packaging of the tools and utitlites, or in red hat's case, what they do to the software. but thats another rant.
now for a linux distro, i would personally recommend buying a book with the linux cd's already with it. might be a release or two behind, but enough to get you knowledgeable to apply concepts to whatever distro you decide on using
