MS Word for me, although I have tried Scrivener and can see the value of it.
For a barebones text editor, I prefer Textpad or Sublime Text slightly more than Notepad++ (not so much for writing, but I am a computer programmer in my day job, so I use text editors every day). I have even been known on occasion to use the UNIX "vi" program to stealthily write novel chapters at work, because it makes prose look the same as computer code.
"I've stopped giving advice. Even when people ask for it, they resent getting it." -Ross Macdonald.