Hi johnmon, welcome to ITKE.
May I ask why are you asking this? Are you looking for recommendations? or is this for statistical purposes? or something else?
It all depends on what you are using it for. There are some out there that are very good for penetration testing, BackTrack, and then there are others that are good for simple use, especially for beginners, Ubuntu. So, you need to figure out what you need and then look for what you want.
To start with linux Ubuntu is the most friendly. When you have more experience with Linux and commands i suggest debian