I had good luck with Uber last month to and from SGN. Set my pickup location, specific to the pillar and the driver pulled up about three minutes later and I flagged him down.

The return from the hotel to the airport was a little iffy since the Intercontinental has two entrances (one for the hotel and one for residences) and of course he went to the hotel entrance.

Fares were about 100,000 (IIRC, I'll have to go back and look) for Uber Black each way. Got Kia Rondos both times so not exactly high class but the drivers had no issue following the directions and were generally friendly. I prefer not to carry cash, especially on my way to the airport leaving the country so using Uber is perfect for me.