I was going to tell you that either of these is just a barrel swap but you already seem to know that.
Personally, I think the .357 Sig has a lot to offer. An attempt at .357 magnum ballistics in an auto-loader and all. But, due to price/availability, I wouldn’t touch it unless I intended on reloading.
I mostly purchased a .40 sig 226 to have a gun in that caliber. Its a high quality firearm and fun to shoot. However I think I like the .45 better. Perhaps because I’m used to the .45.
The .357 sig is a good round and according to the tests I’ve read it only beats the .40 in performance by a very small margin. For me that margin was outweighed by the availability of ammo.
There are differences in handgun rounds but it I think it depends on what type of shooting you will do. If you are a cop who is likely to shoot through car windows or doors then you want a round with a little more speed and weight. The 9mm tends to perform poorly when it hits windshields or other hard barriers. The .45 is a little slow to penetrate a metal car door dependably. It can also be slowed by heavy clothing enough to limit its ability to do significant damage.
The .357 sig and .40 S&W have both the weight and energy to penetrate and retain sufficient energy to create a significant wound in the target.
I live in Florida where heavy leather jackets are rare and I doubt I’ll be shooting into cars. For me the .45 acp is preferred except its hard to carry concealed in shorts and a tshirt. I plan to get a small .40 that I can carry concealed.