In choosing between IA Writer and Ulysses, what features do you value in your choice? (Leaving the sub out of the discussion for the sake of evaluating quality matters).

iA Writer and Ulysses are apples and oranges. iA is a very competent markdown editor. Ulysses is more of writing environment that incorporates a good editor. If you're writing long form, or a paper, or even a book, Ulysses is the place for that because of its library and file management.

I agree with Paul. If you've tried both and are still unsure of the differences, then you're probably not using those extended features of Ulysses that Paul references, which means you're probably better off with iA Writer since it is cheaper.

For longform writing I value my own choice of fonts and background colors, which is why I mainly stopped using IA Writer years ago. I purchased the IA apps in 2017 ($9.99 for the Mac app, $3.99 for the iOS app) and made good use of them for a long time. But I do not like the binary choice of light or dark theme, nor the restriction to their idiosyncratic allowance of only three embedded fonts of their own making. The devs made these restrictive choices on purpose, and they've lost some sales because of it.

Indeed, IA is so hamstrung by their own font limitation that they utilize their own proprietary (yet generic) serif and sans serif fonts on their own website, which they refuse to allow to be used in their app.

Otherwise IA Writer is good at what it does. I find that for Markdown, for me Drafts beats IA Writer on Mac/iOS in most ways. It's more robust, it feels faster, it comes free, and the unlocked version let you choose from multiple themes.

For just writing text on Mac I've used BBEdit for literally decades. Rock-solid, fast, with excellent GREP search/replace. It's another app that can be used for free, and if you aren't coding you probably don't need to pay for it. (I do anyway.) And it is infinitely flexible in your choice of fonts and colors for... everything.

My main longform writing app is Ulysses. As others have mentioned it's quite different from IA Writer.