The app I use most of the time for layering, masking, and blending is Leonardo, but it hasn't been updated in 3 years, so even though it still works, its days are numbered and it wouldn't be a good buy. Its successor is Superimpose X, which does the same layer/mask/blend things but is laid out a bit differently.
Turn your ideas into beautiful works of art using Superimpose X, the new version of the Superimpose app. If you can imagine it, Superimpose X will provide the tools to do it. Packed with wide range of editing capabilities from multiple layers, blending modes, masking, adjustment layers...
In SX, I set the pref to "use old interface" which gives me tool layouts and looks that are closer to Leonardo and so more familiar.
But other people probably have their own favorites. Starzee