It seems that too often, people assume that the amount of blast and recoil that a person can tolerate whilst still shooting proficiently is universal, but it isn't. I've known people who could manage a .44 Magnum so well that it put other shooters with 9mm's to shame and I've known other people who could barely manage anything bigger than a .22 Long Rifle. To say that anyone who cannot handle a .357 Magnum simply needs to train more/better is a fallacy because we do not know if that person has an ailment that prevents them from tolerating .357 Mag recoil, if they carry a gun so small as to make the recoil prohibitive, or if perhaps they have small hands and cannot get a firm enough grip to handle a lot of recoil.
However, it is just a large a fallacy to say that because the .38 Special is easier to shoot and has less recoil, that the .357 Magnum is a poor choice for everyone. The old, and probably best, advice is to carry the most powerful gun that you can shoot well and carry in a practical manner. Recoil and power are a balancing act, so much power that recoil is prohibitive is just a bad as so little recoil that power is inadequate.
Now, some will argue that a smaller and/or less powerful caliber like .38 Special or 9mm is the best because they are easier to shoot than a bigger and/or more powerful caliber like .357 Magnum or .40 S&W. They will argue that placement and penetration trumps everything else so the larger calibers offer no substantial benefit. I would counter this by pointing out that even smaller, less powerful calibers can penetrate adequately with the right bullet and be easier to shoot as well. I'm pretty sure that you could hand almost anyone and full-size handgun in .22 Long Rifle and they would be able to shoot it faster and more accurately than a comparable gun in any larger caliber. If we want to stick with a centerfire cartridge, something like the S&W M&P Shield 380 EZ should have less recoil than a 9mm and a revolver shooting .32 S&W Long is quite easy to handle.
We don't, however, usually recommend small caliber like .22 LR, .380 Auto, or .32 S&W Long to non-recoil sensitive shooters because their light recoil is outweighed by the ballistic advantage of a 9mm or .38 Special. While most anyone can shoot a small caliber better, most can't shoot it so much better to be worth the decrease in terminal performance that they offer.
So, as I see it, a person who is proficient with a large and/or powerful cartridge like .357 Magnum or 10mm Auto isn't really well served by going to a less powerful caliber that they shoot only slightly better. Of course, proficient, adequate, and slightly are all subjective, so I would put it this way: carry the most powerful cartridge that can be had in a gun practical for you to carry and that you feel confident in your ability to shoot well.
