I used both Google's speech-to-text APIs and Assembly's APIs as well as some other ones to build Twilio Voice phone calling applications. The out of the box accuracy was way better with Assembly and its far easier to quickly customize the language model for higher accuracy in specific domains (for example programming language keywords). Generally I avoid using Google APIs whenever possible since they always seem overly complicated to get started with and have incomplete documentation even when I'm working in Python which should be one of the better supported languages.