The two major platforms are Blogger and Wordpress.
Blogger is owned by Google. It is easy to use but is limited. I observe that the majority of history blogs use the Blogger platform. Ease of use seems to be historians' major consideration.
Wordpress is the heavy favorite of successful bloggers in business and other subjects. It has a variety of features that enhance the blog posts. For that reason as well as superior appearance, it is what my blog uses.
Here is an example of what a post looks like on blogger.
And this is the same post on Wordpress.