The Diablo/Nox perspective would be more difficult to program and you will have more programmatic considerations if working with it. Diablo/Nox is isometric or something close to it.
My advice is to start with something like A Link To The Past. It is considered an "oblique" projection:
https://upload.wikimedia.org/wikipedia/commons/4/41/Graphical_projection_comparison.png (bottom right)
I have experience making art in the oblique perspective. My opinion: I am rather slow, but regardless, it seems like it is more time-consuming than sidescroller art, for example, due to the perspective. But games in this perspective usually have more of a world to explore, as there is as much interactive content in both the x and y planes. In sidescrollers, much of the content is concentrated along the x axis, with sky and background taking up much of the y.
Probably one of the first issues you will run into is this: how do you render going "behind" a tree and in "front" of the same tree? This is a simple programming problem with multiple solutions, but this is one of the things that you will deal with when making a game using this 3/4 oblique graphical projection.