I recommend a blog with your own URL (WordPress or Ghost). Then you can syndicate to Medium and Twitter with plugins. That way your content stays yours and you remain in control, while also getting the exposure from other platforms.
I don't remember the exact number, but the vast majority of my Medium readers (something like 80% IIRC) came from HN, Reddit, Twitter, etc. My most read article had about 170k reads before I removed my content from Medium.
* Edit: That doesn't mean you shouldn't! :-) However, you might get more readership - if that's what you're interested in - by writing pretty much anywhere, and just sharing it with the right communities.