Blogger:

Blogger is service which is freely provided by google and anyone with non-technical skill and easily and conveniently use it and create blogs. It is secure platform.
But there are some limitations with this platform as it have basis blogging tools and doesn't  add new feature. It doesn't update.

Medium:

Medium's growing popularity within bloggers, writers, experts and journalists. Its very easily to use platform with social networks feature. It is reachable with same interest community. if you lose audience means losing all followers as medium owns your audience.