Neither?

Amazon sounds like an absolutely terrible place to work, and I'm not convinced it's going to be stable or long-term lucrative for someone just entering the job market now.

I don't think a masters in CS is going to buy you flexibility and money in the long term. Specializing further is the opposite of flexibility. Staying in school longer carries an opportunity cost, and a masters doesn't increase your salary much when it comes to software.

(And if you're aiming to be a Big Deal at an AI lab eventually, a PhD would probably be what you want.)

Do the masters if you think you'd enjoy that particular experience. Go out and find a job of you think you'd enjoy that more.