Glock 26, 27, or 36. I have the 26 and 36. Also have a 19 but seldom carry it since the 26 followed me home.
Get what you shoot well. If you can't double tap with it, try something else. Handgun ammo sucks. All of it. Being able to get a second shot on target quickly is important.
I double tap 2" apart with the 26 as long as I pull the trigger as fast as I can (~1/4 second splits). If the first shot is in the IDPA COM circle, so is the second. The dynamics of that gun are just right for my hands, arms, and grip. The 26 double taps better for me than the 19 or the 36, but the 36 is new to me and I need a lot more practice with it.
A different gun might work better for you. The only way to know is to try them. Not one or two rounds, but a couple hundred rounds. IMO a 9mm you do good double taps with is better than a .40 or .45 you can't do good double taps with.
That said, a .45 you do good double taps with is better than a 9mm you do good double taps with. And so it goes.