This will come off as arrogance, but I don't feel like you have any kind of technical experience. "Looking cool" has nothing to do with the OS, programming lang

This will come off as arrogance, but I don't feel like you have any kind of technical experience. "Looking cool" has nothing to do with the OS, programming language or technology stack you're using. Now, to answer your question: pick whatever you're most comfortable with. Software startups fail not because they are built with PHP instead of NodeJS, but for entirely other reasons.