Groovy/Java has the best support since it is the technology stack upon which ReadAPI is built, so you can use ReadyAPI libraries or 3rd party, including your own.
I would also appreciate Python support as it's easier to learn and has much broader support (libraries, trainings, documentation). Groovy knowledge is quite rare amongst users (who are not Java developers) and some customers tell me they even cannot find a suitable Groovy training.
But if you want to wrap a ReadyApi test run in a python script I'm very sure you could work something out using the CLI of ReadyApi. We do that to alternate between Serial communication and Rest requests.