If you're going to do videos like demonstration and the like, I would hands-down go with the 70D. Unless you have a friend, a third arm, or you're an octopus, you'll definitely need the auto-focus of the 70D when you hold up items to show the viewers/camera. It'll be hard to focus the camera with one hand and demonstrate a phone or something with another. Also, the low light powers of the 6D are of course better, but you don't need anything extreme indoors, especially with sufficient lighting. I'm sure you wouldn't be shooting at night with your small light on anyhow and even then with a 6D, wouldn't look that great.