I've been thinking about how to answer your query and I'm pretty sure that I'm not going to answer it satisfactorily, but I'll try.
It is not so much a question of IWB or OWB as it is a question of wardrobe, habits, environment and build as well as other factors.
You have to look at what you will be wearing when you are carrying and what will it cover. It may be that you will have several holsters that you alternate between to meet what you are wearing at the time.
Personally I alternate between a pair of Galcos, one is a small of the back and the other is an avenger. Both are OWB, but then my wardrobe usually allows for something to hang down the couple of inches that both of these extend down below my belt. The differences in them for me is that the SOB centers the weight on my belt better, allowing me to carry with greater comfort (and we are talking about a full size 1911) for longer periods of time and I can present faster from the SOB than I can from the Avenger (perhaps a bit of an anomaly but that's me). The Avenger offers me a bit more security for crowded areas because I can very casually hold my elbow on it and prevent any but the most determined person from putting their hands on it.
I will likely be adding an IWB to the pair though as both of them, while comfortable and secure as well as easy to get to, require a wardrobe that allows something to hang over the top of them and my movements have to be restricted enough so as to not pull up on the garment revealing the muzzle. An IWB would resolve that, but it would be a trifle more difficult to present from. I'd also need to ensure that my waistbands were a bit more relaxed as well. the IWB model that most appeals to me is another Galco, the NSA II. I like it because the belt clip is less conspicuous than the others and since it is off the center line of the gun, adds less bulk.
Those are what works for me and why, but you will have to look at what you wear and how you wear it before you can take into account what might work for you.
