It really depends on what I need.

As a writer, Ulysses, Bear, or Scrivener, or NVault, because I do not want to deal with formatting beyond the basics via markdown, when I am writing, since I concentrate on content, rather than on form. Later on, I can export into professional-looking formats, depending on my needs, such as pdf, epub, etc.

As a student, things are a bit different. I want to handle citations, footnotes, endnotes, and jump back and forth between the various elements, here the structure is very important from the start, so Pages. Editing is also easier with the structure in mind, I've recently edited an anthology of short stories written by many authors, and exported to epub without issues.

As a programmer, I do not need formatting, but I do need autocompletion, the ability to jump between various functions in a source file, jump to line numbers, execute a compiler and see the results through a pipe, so here TextMate is probably one of the best.

If someone tells me something I should write down, I am more likely to open TextEdit or TextMate, because it's the easiest to reach and use, I can always move my notes to an application designed for notes later.

If I need to share any kind of text, a self-hosted pastebin instance is my friend, though if you are not conscious about your data, or you don't care, you can use the many hosted pastebin solutions out there.

As you have guessed, this is a very complex thing, and it depends on a lot of factors. The main thing is that all of these are accessible via VoiceOver.

I used to use Pages for everything, it can read Word documents and export to Word files as well. It's accessible for the most part and syncs with Pages on my IPhone really well. Lately however, I've been writing in Scrivener. It's great for me, but it's mainly designed for writing novels and scripts and other fiction type things. It's accessible and I love it. But if your looking to write a resume or report or memo or something you're better off with Pages. But for any fiction writing or creative nonfiction Scrivener is the way to go.

TextEdit is super versatile. I use it for most word processing and coding, and also use Xcode for programming. Can aesily use Pages or the latest version of Word for reading and writing and stick with those if I need to write something out as a .Docx file, but mainly I just stick with TextEdit.

Back in my mac days I just used pages for all my word processing needs, and text edit for notes and other simpler documents.