I have over the decades tried every combination I can think up or have read about for designing things and I always land back in the same place, A4 5mm square pad (cheap but not the cheapest) and a really good (but not expensive) set of ballpoints in black/blue/red/green (and mostly it's black anyway).

There is something about the complete free form nature of pen and paper that makes me think better, I bought a nice ipad/pencil a few years ago thinking that would replicate it but it didn't, it was closer but not close.

If it's something I want to keep I just take a photo but vast majority of notes are transient anyway.