Fidelity

Fidelity is the biggest US retail broker by AUM but my god it is awful to trade there if you do anything more than buy and hold or very simple options strategies. Futures are straight up not offered, doesn't even have an official API in 2026, and odds are that one of your 401k/IRAs ended up there so that's mixed blessing depending on if you suck at trading or not since those barriers that deter active trading also put a wall between you and your money so you don't receive one of their famous "Are you sure your investment objectives are being met? Because your port is down 80% in the last month." letters.