In the cooler months with the 'extra' clothing it's easy, and pretty comfortable, to carry in a sholder rig. For me down here in south Georgia/north Flordia I won't wear too many 'extra' clothes too often......so most of the time an IWB or OWB holster is the way to go for me. On long trips in the car, during the brief 'cooler' weather, or when 'dressed up' (sometimes) I'll grab my sholder rig and go.
I love the sholder holsters but my method of dress keeps it's use somewhat limited.
Most IWB holsters are, for the most part, 'easier' to take on/off and they do an excellent job of concealing/securing any sized handgun. A quality 'tuckable' style IWB holster can make even a 'larger' handgun dissappear.
IWB holsters have the edge over sholder holsters due to it's easier to find/order them, thier 'usually' cheaper, and can be worn in many more situations than a sholder rig. Now this is just my observations and by no means the bottom line to your querry.
I took my time and got, for me, the 'right' IWB and sholder holsters.