Be nice. Or else.
underscores.me is the one that I recommend.
Clean and easy to customize.
When I start building themes, this is the template I use.
If you're new to building themes, I recommend building a child theme or two on top of TwentySixteen or other default themes first. https://codex.wordpress.org/Child_Themes
Thanks guys. I actually build my own themes quite often (usually using Bones as a starter framework), but am looking for a pre-made solution this time. I'll bookmark this one.
One step further, components.underscores.me starts you with a basic layout.