If you are in a car all day and wearing a suit jacket because the bosses said so, then the shoulder holster is a lot easier on your back than a belt rig pushing your kidneys for 10 hours of driving. But with a large gun on one side and handcuffs or spare ammo on the other side, and you are doing a lot of walking around, your shoulders feel it the next morning.
In a tussle with a suspect the shoulder holster gives the suspect much more opportunity to grab your weapon than does a weapon carried behind your hip.
Running and jumping tests the retention catch of your shoulder holster. I used to use a comfortable rig by Cobray, but with several weapons (Sig 228, 1911, and Ruger Service Six (the rig was modular and each had their own holster)) I found the as bought set up insuffient when it came to retention while vaulting fences, etc. The solution for all of those holsters was to add a second snap. I had no more gun dropping out or sliding issues after that 2nd snap was added.
I should note one of my old agencies had a requirement issued by the General Counsel that each new holster type had to both be approved by our armorer, and the intended wearer had to qualify PPC with it being while worn in the fashion intended. Back then for reasons of range safety there were a lot of Police ranges where shoulder or ankle, belly band, thigh, etc. holsters were not permitted. Finding or scheduling the PPC qualification test was sometimes fun.
A lot of the answer depends on what you will be doing that day and what is anticipated. Driving a car 300 miles to hand deliver a package, executing search and arrest warrants, going to the supermarket with the kids, carrying a bag of money down the street and through a crowd as an armored car guard (you want a belt rig with a secure firearms retention), rappelling off a roof, greeting visitors as an armed receptionist, going deep undercover while armed, etc. There is no always correct method of carry.
