Notability contains tools for typing and handwriting text. Unlike many apps that contain pen and pencil tools, Notability’s pen tool is smooth and responsive to the Jot Pro Stylus pen I use. The pen tool can be used for sketching and writing.
I'm a total sucker for note-taking apps on my phone and iPad. Although I have many of these -- so many I'm scared of counting them all, Notability is my favorite thinking and brainstorming app.
My other favorite is Drafts, but I rarely use it to think and plan. I use Drafts primarily for creating content away from my computer. That content's sent to Evernote. (I don't create text directly in Evernote because Drafts is faster.)
Notability is fun; try it and see.