Firstly, I like WP, and I like it a lot. I think its the most appropriate choice for a large, large portion of the net. But I intend here to make the argument that it isn’t best choice for CI’ers. I’m obviously biased, so take everything I say in that context.
There is a free version of EE (“Download Free Core Version” on the homepage).
If you intend on using pre-created themes, then its hard to argue that there aren’t many more available for Wordpress. Sure, many of the popular ones have been ported to EE, including Hemingway, Ocean Mist, Salmon and many, many more, but at the end of the day there is more choice in WP. That said, I don’t see being able to use other people’s designs as a particular strength. For me a blog is both a place to post writings and communicate, but also an expression of the developer. I like what the WP guys do, but “Kubrick” is not how I want to express myself. Neither is the pre-built EE theme though. I suspect most Igniters want to do their own design, and if so, who has more themes is a non-issue.
So if you agree with that point (and I concede that some people aren’t interested in design, making this paragraph moot), it boils down (in a design sense) to which one is easier to customize. For anyone on these forums, this is probably a draw. Everyone here is highly technically skilled, and it might take a few extra minutes one was or the other. That said, I’d argue EE is easier to design for (you can organize templates, page structure, etc, however you want), and I’d certainly argue its more flexible.
Changing the design after the fact? Big plus for WP. It has 1 click theming, which EE eschews in favour of flexibility and power.
Community size - big plus WP. But we could make the same argument of Zend over CI, yet we’re all still here 😉 The EE community is very similar to the CI community.
There are 2 compelling reasons that I can think of in favour of EE for anyone reading this. (1) Security (EE vs wordpress); (2) The fact that EE and CI are so tightly ingrained. More and more EE code everyday is merging with CI, so as a CI developer you can leverage your skills to build with EE, and vice-versa.
Plus, EE is a full on CMS - if you ever want to grow out of a blog, or get hired for freelance and need a content management system, escalating up is very (trivially) easy.
Again, I like WP, and I like what those guys are doing. I’m not trying to say WP is not as good as EE, but rather, that as a CI programmer EE offers you benefits that WP can’t.