as has been said, uber is now gone from thailand, and GRAB is the only options. I have used GRAB many times - usually when I cant flag down a regular taxi. In Bangkok GRAB is mainly used by the taxi drivers to help them find fares - works well for them in outer areas - where they can do a drop off and usually collect a pickup pretty quickly.
Grab also works in Pattaya - but it is grab car not grab taxi - same app though