This is a no brainer type of question. I'd pick the red door, because it's hard enough to make $1 million these days, but with $50 million you could do so many things in the world and buy whatever you pretty much want.
I don't see the point in going back in time since there wasn't as much technology back then as we have now, and there wasn't that much to do in the past anyways. But with $50 million, I could buy so much technology such as consoles, phones, computers, etc or start my own major tech company as well. It's better to live in the future than in the past anyways.