I find AIWB to be the safest, fastest and most convenient way to carry. Straight drop works best for me so the grip stays closer to my body and prints less. I now have an "extended barrel" holster for my Shield, not only because I DO have an extended barrel, but also because it is longer and therefore the top tips away from my body less.
Carrying at 4 is harder to conceal, access and control (from a grab) IMO. Also, it can only be accessed with one hand. The covering garment is harder to clear than with AIWB. Very difficult to access when seated (and uncomfortable), especially in a car. AIWB overcomes all these disadvantages.
I put a long strip of loop velcro on the back of the holster to make the rig even more comfortable, although the Shield is smaller and easier to conceal compared to my regular EDC Full Size M&P. With the velcro strip on the back, I can glue a mating piece of hook material to a closed cell or gel foam pad to put at the bottom of the holster, which aids in comfort but more importantly keeps the grip tighter to my waist.
I just received an AIWB holster for a Glock 19 that has the (removable) "wing" to help keep the grip in against my waist. Works well. I'm not sure it is necessary for a grip as short as the Shield when carried AIWB, but it might help. Even carrying my extended MagGuts + 2 mag (10+1 in gun) my Shield grip does not stick out. I have more real estate at my waist than you do--36".
My latest holsters have come from
JM Custom Kydex