I started programming in Flash (after doing some basic html/css), and have later done some stuff in Processing as well. Flash was an infinitely better tool to get started with programming because it lets you actually draw and animate vector graphics, and then sprinkle in a tiny bit of code to make things interactive.
Compare that to Processing, where even just using some images drawn in some other tool is more difficult than it should be. I don't think you can really even compare the two in terms of beginner productivity.
In that case, I think Unity fits the hole that Flash used to fill. You can copy a bunch of free assets from the store (or build your own using blender) and then sprinkle in some code to make a game.
Compare that to Processing, where even just using some images drawn in some other tool is more difficult than it should be. I don't think you can really even compare the two in terms of beginner productivity.