If he hits first he can teleport or time reverse Surtur and wins. If Surtur hits first with a fire beam Strange dies because he is just a regular human and his shields wont protect him from the heat that will melt his face off.
So whoever hits first wins. Depends on the scenario. If they are both starting in the same moment and will use maximum speed from the start then Surtur should win. His fire beam doesn't seem to be needing any time to cast and Strange needs time to cast every spell, including the ones from the eye.