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Well, it depends really on your needs and what you are going to use it for.
However, I already took a look behind the scenes of a couple of these CMS systems, and if you want a free (or at least, very affordable) CMS system, then Mambo Open Source is the king of the Content Management systems.
As long as you do not intend to do extremely complicated things, you will get to love Mambo. Well, even if you intend something complicated you can have someone program it for you (or yourself if you have skill), it's open source after all.
It is a very easy install as well, regardless of whether you use a Windows or a Linux webserver.
Mambo has a demo website, where you can test the functionality of the CMS, but unfortunately you cannot post links any longer...
So 1 more vote for MamboOS.
I spent a few hour with TC CMS yesterday only to rip it out. I just couldn't get the look flexibility that I was hoping for, and that seems the major drawback to most of them.
I have a new client that needs to edit only text and am probably going to just go with Contribute 3.0