The sun would always be just on the horizon 24 hours a day on every day at the poles. Every day would be like what it currently is on the equinox since every location on Earth would have about a 12 hour sunlight days and the noon sun angle would be about the same every day. An Earth without a tilt would be stratified into climate bands that would get progressively colder as you moved away from the equator. Humans would never survive the continuous winter of the high latitudes, and so we would likely congregate in the planet's tropical midsection.