I’ll be giving JetBrains Mono a try, but for the past few years I’ve been enjoying Dank Mono[0] for writing Swift, Obj-C, Kotlin, and C#. In particular I like its handwriting-inspired italic style, which works well for adding contrast to things like keywords.
I also use dank mono and really like it. Its similar to JetBrains Mono and Roboto Mono, but a bit crisper and slightly more space efficient. Looks equally good on my Mac retina display and my Windows 1080p display.
[0]: https://philpl.gumroad.com/l/dank-mono