Hello!
To know which one we would smell first, we need to know which compound is the most volatile. ¿How do we know that? A useful data is the boiling point. The boiling point is the temperature at which the compound goes from liquid to gas. As the boiling point is lower the compound is more volatile. The boiling point of NH₃ is -33,34 °C while the boiling point of C₂H₆O (Ethanol) is 78,37 °C. So, Ammonia is more volatile and thus it will be the first compound to be smelled.
Have a nice day!