Total 3pointers Made in a Career
When people say something like "Curry is the greatest shooter ever," they get to say this confidently primarily due to the following stat: total 3pointers made in a career. This tactic would often be effective in winning arguments, but it assumes the other person doesn't know or care about the history of the NBA.
The other number that is convincing in arguments about shooting is the percentage, of course. But the shooting percentage is not a reliable way to judge this either as the circumstances of each shot is highly variable. Fundamentally speaking, only the free throw percentage can be somewhat treated scientifically. Fortunately for Curry supporters, his FT% is at the top of history so the argument is strong in his favor. However, there are many shooters I would prefer historically over Curry for other reasons.