I once waivered between markdown and org-mode. But the ecosystem of Emacs packages that build on top of org-mode is mindblowing. Tables with formulae, inline programming (in your language of choice), back links, PDF annotations, bibliography, automatic conversion to HTML/PDF/LaTeX, still unmatched repetitive tasks in TODOs, even simple text collapsing, and so much more. And none of this weighs down your particular setup because you just ignore what you don't use and it never loads!
I personally realised that I'm never going todo any serious editing on my phones so Orgro/Orgzly work very well on Android. And since everything is plaintext, any org file can be opened in any editor and edited normally. I have a simple editor app from f-droid which works very well.
In this folder I categorise with subfolders and use simple markdown files to write down stuff and todo.txt for when I need tasklists. A dedicated file in root is used for collecting random stuff before there get sorted and another to collect all links that I wanna bookmark.
This works very well on different types of devices at the same time. On android Markor is a good editor for it, on desktop/macs I recommend typora for the nice interface and obsidian.md for the nice navigation between files, if you don't have already have setup a favourite editor. Also works well with vim/emacs/vscode or anything else that handles plain text files.