Well, .45 ACP has seniority, as my first handgun was a 1911, in late 1982 or early 1983. I had previously owned a 9mm Uzi Carbine, but though it fired a handgun cartridge, the weapon, itself, was a rifle. So, I will list .45 ACP first.
I cannot remember whether .38 Special or .357 Magnum was next, as I bought an S&W Model 60 and an S&W Model 581, later in 1983, as I prepared to start a police academy. I favor both, but reckon that I have a special consideration for the .357 Magnum, because the Ruger GP100 is my absolute favorite firearm, of any type. Not only is the GP100 a perfect fit, for my hands, in every way, but I used one to defend myself and others, one night in 1993, so I know the damage that a 125-grain .357 Mag projectile will do to a human opponent, and the same cartridge is available with various bullet weights and types, to do just about everything that has to be done, with a handgun, in the Lower 48 states.
I favor .45 Colt, too. Mild to shoot, this one does little to vex my aging joints.
If I had to narrow it down to two, as was done in the original post, I would reluctantly specify .357 Magnum, and .38 Special.