Reggie Miller, Ray Allen, Kyle Korver, Klay Thompson are all amazing shooters and all legitimate candidates if you picked one guy to make that last second three. They all made spectacular shots made in their career and are amongst the best shooters to ever play in the NBA. With all that being said, Steph Curry is the best shooter of all time. Period.
Not to get into ball handling, playmaking etc (but notice Steph is the only PG in the group), just considering shooting the ball, Steph is the best one ever. He has unparalleled range, the quickest release and can shoot off the dribble better than anyone else. His shooting creates the most gravity and influences defense out of any other shooter ever. Even with KD on the Warriors, their single most important player is still Steph, he still has the biggest +/- of anyone on the team. During his amazing '15/'16 run when he became the unanimous MVP, the questions was what else can he bring to the table? The talk around the Warriors is that his mechanics allow him to expand his range significantly beyond the line and that soon defenders will need to pick him up from the half court line.
The shot he made yesterday will not be featured as an in-game strategy for the Warriors, but after all the shots he made, when he lets it fly you kinda go "Yep, that one's going in." Maybe this becomes a standard in his famous pre-game warm-up session, who knows. If there were a line in Vegas: will he make 10% of these during warm-ups in the entire regular season....would you consider it? There's your answer.