I still use plain text for everything. (2016)
Apple Notes is my go-to for “almost plain text.” It’s simple, instantly syncs across phone/desktop, and I can throw in bulleted lists, photos, PDFs, or whatever else if needed. I have meeting notes, to-do lists, journal entries, and god knows what else in there.It’s not perfect - Markdown, or at least code blocks, would be nice, and tags (I think those are coming in the next OS release), but in terms of ease-of-use, I haven’t found anything close.