Hi, I'm new to bitcointalk.
I'm only 15 years old and I'm Brazilian, I want to know which is the best long-term investment.
for the next bitcoin halving

If you are already anticipating for the next halving then why not simply hodl bitcoin as you wait. There are lots of project that might have promissory ROI but to be on the safe side and avoid falling for scam project stick to Bitcoin except you are willing to do your personal research on other projects.