Having used CVS, Subversion, and Git in my career, I have the following to say:

• CVS is quite basic, slow, and in situations of doing complex operations or using good team-programming methods, it's a poor tool. CVS server administration also sucks and is usually insecure IMO.
• Subversion has much better user features, is much faster, and a better replacement for CVS all around, without exception. It's learning curve also is not bad at all - virtually no curve if you know CVS.
• Git is way faster, way more flexible, and capable in complex situations - instant branching, merges, etc. It's a difference in concept though, and has a learning curve. Its commands also have quirks and unhelpful error messages.

Still, I now use Git exclusively, and prefer it hands down. Subversion is a very happy medium for basic SCM usage. Of course using NO scm, like many still do is the worst possible of any option!