Math says so.
Mathematically is proven. Billions of simulations were done in computers, so we should trust basic strategy and math. It would be impossible to explain your question and prove mathematically right now. But in order to answer your question at least partially.
In table below is represented mathematically your expectation. These numbers are already calculated and proven and you should stick to them. Bolded are best expectations.
(A,3 vs 6) stand (-0.14357) hit (0.140795) double (0.189743)
in this case double has the biggest expectation for you even though it is such a small difference in between numbers. Same goes for numbers below
(A,3 vs 5) stand (-0.15483) hit ( 0.117682) double ( 0.144734)
(A,4 vs 4) stand ( -0.20038) hit ( 0.059483) double( 0.06443)
difference is so small in this case 0.06443 - 0.059483 = 0.004947 , but still it is a better choise to double.
Basic Strategy is like that if you observe every single rule, edge against you will be about 0.5% on average. Not observing all of the rules or playing partially correct basic strategy will cost you 3% - 5% of the money wagered in a long run.