First, please tell me which is the best country. Then tell me which is the best religion. *Then* I'll tell you which is the best CMS.
Okay, cancel those requests and that promise. We try to avoid specific tool recommendations, but even if we didn't, you would get no answer. You would get 50 answers. The best thing to do is simply to try out several and see which one best fits your need.
I have tried perhaps a dozen. Every single one has post after post in their forums saying "Finally! I've found the best CMS ever" and post after post saying "Your CMS is garbage." The couple that I like have many detractors. Some of the most popular CMS just seemed terrible to me.
Part of which is best depends on what your needs are, part depends on your skill level with the underlying language used to code the thing, and lots of it has to do with how you think and how you approach a problem.