I would include Roy before his chronic loss of form, many times he literally crushed the opposition within a few overs.All 3 are good and top class Hales, Buttler and Bairstow.
Stats are of course a guide but Buttler imo is the best, all 3 can score very quickly but Buttler the best at assessing pitches/conditions etc and the game situation.
I would say Buttler is the best T20 player we have ever had never mind just best one now.