An IWB is worn so that the top of the frame/barrel rides just behind your hip bone. Typically, that's about 4:30. The further back, the steeper the cant needed to get a comfortable grip when drawing the weapon. IWB holsters typically have a 15 degree cant. The most comfortable IWBs have a wide backing to distribute the weight, and two belt loops for stability.
You can't go wrong with a Sparks VM2 for pistols or revolvers. They have a wide, smooth back, made of horsehide for moisture resistance. The wings are flexible, so they mold to your body. The loops are attached with two screws, so they can't rotate or loosen. The mouth of the holster is reinforced with a steel band, so they don't collapse. That makes drawing smoother and enables one-handed re-holstering. The downside is the optional Kydex clips for tucking are very hard to use.
For tucking, I prefer a folded type holster with a single wide loop on the rear wing. The best one I've found is a Blade-Tech UCH. It's Kydex, but comfortable enough for all-day wear. A single loop is easier to tuck because you don't have to fool with bulges between loops.
I think pancake holsters are the most comfortable and concealable OWB holster. It takes a long overgarment to conceal even a 4" barrel, compared to an IWB holster. A lot of people make good pancake holsters. My favorites are made by Kramer, Alessi or Ryan Grizzle.
For any high ride holster, the shorter the barrel, the better. I'd say 4" is as long as practical. Otherwise the barrel clunks on the chair when you sit, and you have to be a contortionist to draw the weapon. I've carried a 5" 1911, but a 4" Commander works better for me, or a 3" revolver.