I've tried nearly every app recommended here and I always come back to Ulysses. Organizational abilities plus no-frills...just fantastic.
I love Ulysses the way I could publish easily to Medium/Wordpress website directly from the apps.
Surprised this isn't at the top honestly. Yeah, it's a little pricey (it's included with SetApp for $10 per month, though), but it's very much worth the price. I do a lot of writing and this is my immediate go to for anything. Built in publishing tools for Medium, stunning interface, incredibly stable. It does it all.
Around the web
Today, we are switching Ulysses to a subscription model. The short story is this ( tl;dr): Our users expect a continuously evolving high quality product - and subscription is the only way we can truly deliver on that expectation. The following post then, is the long story.
Easily annotate documents directly while reading them with real-time synchronization. No one but you has access to your PDF and annotations. All your PDF files & annotations are stored encrypted with keys only you control.