Control version systems

CVS, Subversion, GIT, Mercurial... I need to see and choose from them.

We are a small business creating websites and we have to implement some control version system.

Which could be better for this situation?

Also, which are easier to install and learn?

#2 does that really work in, like, serious production systems?

Do any of these have some graphical interface to commit changes so web developers don't get frightened?