I use daily Markdown files, which I started out just manually creating, then I used an extension in VS Code called Journal to create them automatically, now I do the same thing in Obsidian.

I have found MD to be the proper mix between formatting and plain text, just enough formatting to enhance readability but not enough to require a mandatory parsing tool. Overall I just consider it essential that at anytime I can take my 4+ years Of daily documents and interact with them in however I want.