I do streaming charity events on occasion and an idea I've had is collaboratively writing an NES game over the course of a weekend, on-camera.
GNU C++ had gremlins for the GBA last time I was writing homebrew for it, so I can't speak to that. I kinda enjoy writing assembly when messing around with this stuff, though, so, eh. For anything else, I love me some (Modern!) C++, but it kind of feels like I should be writing assembly for that stuff, it's more fun to me.
Do me a favor and chew on something for a sec, though: what does your "What?" do except add a hostile and combative edge to the conversation? Maybe don't do that. Thanks.
The NES is a much simpler system. Granted, it's a simpler system that you're programming in a less-convenient language, but I think that which one is "easier" depends on what you're used to.
GBA lets you use C without bank switching. I'd say it is far easier than the older generations.