I took the Sig Sauer Intermediate Handgun skills course with the Sig P320 and was impressed at the start with the trigger pull, I measured it at 7 lbs but very smooth.
It resets itself with a felt click by easing your finger pressure after the shot and now ready for a follow-up. I believe it is a dual purpose pistol at ease for conceal carry though not as small as some conceal carry and it is ideal for home defense.
I can only say that recoil with 115 grain bullets was so mild that it was never a thought that recoil was ever an issue.
The use of an expanding bullet is perhaps the best for self-defense. If I were to carry all the time as a citizen, then I would opt for a shorter frame like the Sig P320 subcompact which holds 12 rounds. But for general use and home defense the standard P320 would be better as the barrel and sight radius is a bit longer. There are lots of pistols out there but this one has won the contract for the US Army making it a very tested product. I had difficulty reloading the new clips provided, common to all 9mm pistols of every make. They do need to be broken in, and loading to 10 or so instead of the 15 during break-in can make it easier on your thumbs. Better yet get a magazine loading tool.
https://www.amazon.com/Maglula-ltd-UpLULA-Magazine-Unloader/dp/B01MQTZVZY
I give the Sig P320 a big thumbs up and it is very cost effective! And it breaks down with a flip of a lever for easy cleaning.
As to whether the 45 ACP is better? That depends on its use and your comfort and skill. Folks have written books on it….
The 45ACP is heavier in general for conceal carry. I have a Kimber 1911 and like it very much but you must remember to cock the hammer if you have it down or to drop the safety lever. But I am used to that.
On the P320 there is no hammer as it is striker fired and there is not a safety lever. It is all in that great trigger design.
If you are going to do competitive shooting then the Sig P320 would be a great choice over the 45ACP.
Keep your firearms safe! Good Shooting!