Which city would probably have a warmer climate one at 20 north or one at 40 South why?

All other things being equal such as elevation, proximity to ocean currents, deserts, etc., the location at 20 degrees north would most likely have the warmest yearly "average" temperature due to the fact that it is nearer to the equator where the Sun's migration is limited to approximately 23.5 degrees north and south annually. The limits of the Sun's annual migration are defined by the Tropics of Cancer and Capricorn.