Blogger
I have been using Blogger for 10 years now and love it for the most part. It offers a lot of customization which can only be said for people who are experienced using HTML or CSS--So a con would be that customization can be hard if you aren't experience with the program. In my opinion, blogger tends to look a little bit less professional, but that also plays into the lack of experience with the website.
WordPress
To me, Wordpress tends to look a lot more professional in comparison to Blogger. A big downfall to me is that Wordpress is that it is really hard to customize. If you want to edit the HTML or CSS of the templates, you have to pay a pretty penny, which I do not like. To me, the best part about Wordpress is the level of professionalism contained within the free-templates. If I had to create a blog for work, I would probably use WordPress.
Wix
Wix is very fun to use and customization is great and can be very easy for those who are inexperienced! You are limited to the gadgets and widgets you can use by having a free account, but I still have had a lot of fun using this domain for blogging. The templates are great and look professional, with some exceptions. There's not much in the way of ability to comment on posts though, which I don't love. I feel like this would be a great domain for a personal website but not as much for educational purposes.
Most Useful for Educators?
I choose blogger out of the three I reviewed. This may be because I've had the most experience with this program, but I feel as though from the student's side of things, it is the easiest to work with, as well as from an educator perspective. It offers all the necessary features that a blog would need for a teacher. You can also adjust it to fit the feel of your class and whatever mood you would like the blog to contain through it's some-what easy customization.