Update, 12/7/21: As an experiment, we're trying out a longer-running Open Thread that isn't refreshed each month. We've set this thread to display new comments first by default, rather than high-karma comments.
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It depends what your strengths and interests are, but let me give some generic thoughts.
Most EA high-schoolers who like math/science should at least consider a CS degree (useful for AI safety research and job security in software development), or a math/econ double degree (useful for Econ PhD, policy, and big picture strategy research). I would recommend that a strong student apply to US universities, because they are far stronger than any outside US/UK/CH. But it's a few months past the deadline for those (and UK universities too). If you're confident you can lodge a strong application to US schools, but you didn't do it this year, then you could take a gap year, and apply in 6 months. For people who dislike maths and are excited about policy or politics, another option is law, which in a US setting could follow an undergrad in some combo of polisci, philosophy, and econ.
I'd be interested to hear what others think too!