If you can’t decide always choose a more excited candidate. You can learn or improve skills, but you can’t learn to be excited about the job. For me, this emotional state is an indicator of a great fit between your offer and a candidate.
Humans are emotional beings, and thanks to our irrationality we can withstand all odds, perform in a stressful situation and overcome challenging situations. And nearly always job requires more work than we thought at the start. You need to have the energy to go through obstacles that will be on your way.
During my endeavours in the startup world, it was obvious after a moment if somebody believed in their idea, or not. Engaged founders were bursting with energy, and if they were doing it right you also get infected with their excitement.
You can do impossible with people like this on your board.