I've been using MarsEdit for just over seven years. I started with version 2, and then upgraded to version 3 in 2010.
Now, in 2018, I just upgraded to version 4. This is my first post with the upgrade and I'll report on it in a little while as I get used to the new version.
Here is what Daniel of Red Sweater Software has to say about his product:
Browser-based interfaces are slow, clumsy, and require you to be online just to use them. Browsers are perfect for reading web content, but not ideal for creating it. If you're serious about writing for the web, you need a desktop blog editor. If you're lucky enough to have a Mac, nothing is more powerful, or more elegant than MarsEdit
Rich and Plain Text Editing MarsEdit's editor switches easily from Plain to Rich Text, so you can work in whichever format you prefer. Love Markdown? MarsEdit can preview it and convert it to HTML if needed.
Wildly Compatible Works with WordPress, Blogger, Tumblr, TypePad, Movable Type, and any blog that supports a standard MetaWeblog or AtomPub interface.
Easy File Uploads Attach images and files directly to your post, and MarsEdit will upload them when you publish.
Media at Your Fingertips Quickly scan your Apple Photos, Aperture, or Lightroom, and insert images into your blog post with the click of a button.
Re-Blog It! Enable MarsEdit's Safari extension. When you discover something cool on the web, start a new MarsEdit post with the click of a button.
Offline Freedom Write when you want to, without an internet connection. Fine-tune your masterpiece on the boat, plane, or train, and publish when you get back online.
Perfect Previews Let MarsEdit's live preview show you how your posts will look before you publish them. Use Markdown or another text filter? MarsEdit will preview that, too.