First off, the statement that svn is not fully stable is blatant nonsense. In fact, svn has been lot more stable and reliable than cvs for at least 3 years.
The quesion "what should I get" can only be answered with another question: What do you want?
If you want to use sourceforge.net (largest free open source hoster) for your projects, then you need cvs. Although sourceforge had already announced to support svn soon many months ago, they still fail to do so.
If you want to checkout working copies for development from a project that is under cvs control (such as Code::Blocks), then obviously you need cvs, too. If you can live with downloading a "release" version, then you don't need anything.
If you can live without sourceforge.net (and use BerliOS for example), then svn is definitely the tool of choice. It is more reliable, easier to use, logical and consistent from head to tail. It does atomic commits (unlike cvs), and many operations that are expensive in cvs are cheap in svn (for example creating a branch takes constant time and constant storage, while in cvs, it takes linear time, depending on the number of sources). Also, unlike cvs, svn can do a lot without accessing the network (sometimes a great performance advantage).
Lastly, there is no reason why you should not have both cvs and svn, they are not mutually exclusive.
In any case, I strongly suggest you get TortoiseCVS/TortoiseSVN instead of the "raw" package, because these tools are a lot easier to use (and in the case of cvs more reliable, too). Also they come with gadgets like conflict editors etc. which are very useful. Sure, you can do all that with another tool (or even by hand), but with Tortoise, everything just works. This is a great advantage.
