I have used Grab (and Uber before that) many times when in Thailand.
I have used it in Bangkok, Phuket, Chiang Mai, Krabi, Pattaya, etc and also to/from BKK and DMK. The experience has been great and I have always been assigned a driver within 10-20 seconds from requesting it.
The same thing can be said about my experience with Grab in Vietnam, Singapore and Myanmar.
My concern derives from the experience with Grab I had in the Philippines last month during my trip in there.
First, it rejected the credit card I had on file with Grab, even though I had used that card with Grab for years in Thailand. I tried with two other credit cards and both of those wouldn't get accepted, so I could only pay with Cash. Even so, most of the times I waited 3-4 minutes for Grab to assign me a driver, only to get a "All our drivers are busy at the moment, retry later." message. Got the same message even after retrying 3-4 times in a row.
Overall, I would say I only got assigned a Grab driver 25% of the times I requested for and that was only after waiting minutes.
Getting a Grab from the airport was mission impossible (I ended up waiting in line almost 45 minutes in order to get a normal taxi).
One of the Grab drivers told me that there are fewer drivers lately in the Philippines and that's why it's getting difficult getting assigned one.
So, I would like to know from the Bangkok residents in this forum or recent travelers if they have noticed the same thing or any worsening experience with Grab in there?
Is it still easy to catch one arriving from BKK or should I book a taxi?
I also noticed in some previous posts that someone has mentioned Bolt is getting popular in Thailand now.
Does that still offer better prices than Grab?