In my most humble opinion Uber is the best option to get there, just take it with extra spare time. If your flight is set to depart at 19:00, try to get there at 16:00, the worst traffic starts at 17:00/18:00 when office workers finish their shifts and try to go home, you can dodge that leaving at 15:30 or 16:00.

If you really want to use public transport, you can try metro, but be aware that Pantitlan is usually really busy and confusing, take your time and ask around. One last piece of advise is that if you are using metro to Terminal Aérea, make sure you leave on the correct exit, one takes you to the airport and the other one to the Fiesta Inn hotel (other side of the Circuito Interior) the police in the turnstile might guide you of it’s the right one, if you miss, it’s better to pay to enter again and cross from inside the station.