Of the sidearm, 3/4, or overhand, arm angles produces the most velocity. Along with control. I throw between a 3/4, and overhand.
As do I. Which is good. These arm angles produce the least stress on your arm and ideal for velocity. As far as control it depends on the pitcher. Velocity depends on your mechanics but 3/4 and overhand are good to stick with. You’ll find it hard unless you are fantastic throwing sidearm or submarine to make it past college.
Great question!! It is not as exact as you might think. The best arm angle to generate velocity is the one where you can put the most force behind the ball. Pretty general, I know. But, if you look at today’s MLB hardest throwers, most come from the 3/4 window or over the top. I like the over the top style because pitchers can incorporate a front side shoulder tilt, helping to produce increased engery and momentum toward the plate. Although, when the 3/4 arm slot is properly performed, pitchers can extend the forearm and elbow in a efficent manner, helping the arm distribute the stress of the delivery.
I do not like the side arm delivery due to safety issues involving the shoulder and elbow. I think a better question might be,“Which arm slot produces the most velocity with the least amount of stress on the shoulder and elbow?” It doesn’t matter how hard you throw, if your durability constantly puts you on the Disabled List (DL).