+1 on what PBP just said.
I will point out that the Galco "Jackass" or "Miami Classic" shoulder holster is one of the most comfortable I've worn. I've managed a 10-hour day wearing mine with a stainless steel Springfield 4" 1911 and loaded mags without undue discomfort. The magazines help balance the rig and keep it from pulling on one side of your body.
The downside, of course, is having to always wear your cover garment. This can present problems if it becomes warm and others are shucking their jackets while you prespire like crazy. Likewise when visiting a friend's house where you want to maintain the cover might look a tad out of place if everyone else is in shirt sleeves.
Horizontal carry is the most commonly found now. If you go this route, as PBP suggested, make sure it doesn't poke out to the rear of your cover. There's some adjustment on the rigs that will help this. Adjusting the rig to suit your size, shape, reach & draw may take time and feel frustrating, but once you get it set up, it's quite comfy.
I think the horizontal rigs offer slightly better concealment, especially if you need to move your arms freely. Most vertical rigs tie down to the belt and can be visible when the jacket gapes open, such as reaching for something. For longer barreled guns (over 4") the vertical rig is usually more appropriate.
Avoid shoulder holsters made of "ballistic nylon" and those with narrow nylon or elastic straps, especially where they pass under an armpit. These tend to bind and chafe.
Because the holster lives near a humid, sweaty part of your body, to keep the leather in good condition, consider using the old spit-shine technique of candle wax. Melt some candle wax and drip it onto the holster, then brush vigorously to spread it around. The wax will help protect the leather from salty body sweat.