Big company or startup for my first GTM job?

The trade is training versus autonomy, and for a first job training usually wins. A larger company gives you a real onboarding programme, managers who have coached before, a working product, defined territories and a peer group you can copy, which means you learn a method instead of inventing a bad one under pressure. A startup gives you range, speed and a much shorter path to responsibility, but a first GTM job at a pre product market fit startup often means missing quota for reasons that have nothing to do with you, and that is a terrible way to learn whether you are good at this. A sensible route is two to three years somewhere with a real playbook, then join a startup that already has some repeatability, where your experience is worth something. And check the quota reality before you decide either way, because early stage quotas are frequently guesses while late stage quotas are set by finance and barely negotiable.