The file is identical
This is worth saying first: an undated planner PDF works the same in both apps. Nothing about the file locks you in, and you can switch later without losing anything you bought.
Organisation and notebooks
If you like a shelf of separate notebooks with visible covers and a tabbed structure, GoodNotes is usually the more natural fit for planner work. If you prefer fewer, longer documents that flow from one section to the next, Notability feels tidier.
Search and handwriting
Both search handwritten notes well now. The practical difference is how each handles a long PDF: check that your planner is fully indexed after import, or a search for last month will quietly miss pages.
The pen feel is personal
Pressure curve, line smoothing and the sound of the pencil differ, and no review can tell you which you will prefer. Import the same page into both and write a paragraph in each before deciding.
Pick by how you plan
If you duplicate pages to build a running archive, favour the app with the cleaner page-management tools. If you want one long notebook per month, either is fine — and the planner layout matters far more than the app.
Where this lives in a planner
Every technique above has a home on the Weekly Planner — Mint Fresh — undated, A4, and ready for GoodNotes, Notability or a home printer. Not ready to buy? Download the free starter kit and try the method first.