Bernie Sanders, but he has zero shot. He'd really shake things up as much as a POTUS could, and his actions to help the middle class would actually meet his words, unlike most.
John Kasich. BY FAR the best resume for POTUS in this cycle. Extensive experience and successes in the Federal legislative, and State Governing Branch, great communicator, speaks plainly, actually knows you have to work with the other side. Just an outstanding candidate even if I disagree with him on plenty of issues.
Both these guys are adults. They don't do the name calling, negative campaigning crap, and actually present ideas, not soundbites.