Outline+ for my OneNote files. I can make and edit my OneNote files and they look the same as on the PC. It doesn't have handwriting yet though, just text.
GoodNotes, for General Notes. Notability when I need a lot of organization but now that I have Outline+ I don't use it as much.
Index Cards for Plotting stories and syncing with Scrivener.
Notes Plus for the side by side screens. Notes on one side, web on the other and I can clip pictures onto my notes, great for research.