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It depends on what are you writing about, and who are your targets.
It depends on the type that makes a blogger comfortable working on. The most popular ones are WordPress, Joomla, Blogger, Movable Type, and TypePad. I use WordPress.
WordPress hands down. It is one of the easiest blogging platforms to run a blog on. It has wide range of features that suits the needs of a beginner as well as an expert.