Also, one of the most critical criteria to decide is job prospects on the startup.
Feel free to share your thoughts especially if you have worked or know the stack in startups. Thanks.
If you are interested in webdev, go with JS first; you’ll need it for front-end and you can get by with it full stack.
Enough JS + React (or Angular or Vue) to do basic SPAs and enough Python + AWS knowledge to build a Lambda-backed API with API Gateway or a Dynamo-backed GraphQL service with AppSync would be a good way to build a portfolio, and isn't really that much to pick up.