From my perspective I'd say use python. yes c++ *can* be faster, but only if you can actually get it to work. in my experience unless you are trying to push the limits of the device, the difference in app performance will be hidden completely by bad programming.
By which I mean you'll waste so much time trying to make c++ work at all, or do anything, that the theoretical performance difference isn't worth much.

of course if you already know c/c++ and are a super clever guy, then go for it. But for me, coming from a java background, I tried C, and it took me ages to get not very far, and I gave up trying to debug my segfaults. I just wasn't prepared to sink my time into getting good enough at C to make it worth while.

Python is *way* faster to develop and get on with for anyone that doesn't start with serious c experience.

In real terms I think I stand a better chance of writing performant Python than I do in C, just because I have a better understanding of what is going on. But maybe that's just me.