On my 12.9 inch iPad Pro with Apple Pencil after trying Goodnotes, Notes plus, one note, note shelf, and notability, it is hard to decide between Goodnotes and Notability.
I prefer notabilitys navigation system for finding and organizing notebooks. The navigation system in goodnotes doesnt give as good of a global picture.
I also wish goodnotes would allow for changing the ink style of handwritten notes that are already written.
I like Notabilitys inking better, but Goodnotes isnt bad.
Goodnotes has better spacing between lines on paper. Notability has an annoying way of presenting separate pages close together in a vertical scroll so that its easy to end up writing something half on one page and half on another. The goodnotes notebook layout is horizontal scroll so the pages feel more separate.
The Goodnotes pdf backup for notebooks reproduces the pages as is, whereas Notability adds a sizable border, which I dont like.