I love all of those apps! Paper was my go-to for *years*; Linea beats it solely because their export tools and background templates are much better (SIMPLE LAYERS, PSD, yayyyy). It makes a lot more sense to me as a basic sketch tool, and has a lot of flexibility to import into another app.
Procreate is my heavy hitter for doing high-level graphics work on the iPad Pro; Pixelmator is its photography cousin. (I live for Pixelmator's repair brush.)
TL;DR: All the apps are great, I just use each for different purposes.