Been there...
I've used mostly DeSantis Slant shoulder rigs to carry a Colt Detective Special, an S&W M36, a Glock 19 & 26 and a SIG 228.
Even the very best shoulder holsters can be uncomfortable unless properly adjusted. The best way to don a shoulder holster without self-inflicted bondage is to hold the rig in front of you, where the back straps cross. Insert either arm while holding the straps, then insert the other arm, returning both hands to the cross straps. Then, lift the straps over your head and guide them to the back of your neck. The motion is similar to how a woman puts on her bra. This helps prevent the straps from becoming twisted.
Safety: With many of you carrying M1911s in Condition One, be aware that when drawing your gun, the muzzle passes over your non-shooting arm unless you train yourself to pull it back and out of the way. But, this is counter-productive as it slows down your total draw and in getting both hands on your gun.
It is better to train yourself to not disengage the safety and having the gun in Condition Zero until the muzzle is clear of all your body parts.
Shoulder holsters have their place but the shortest distance and time from holster to "on-target" is with a strong side belt holster.