I typically carry IWB, strong side. I find it to be the best in concealment. The gun is hidden well by your pants, hold close to your body to avoid bumping things with it, and is quite comfortable with the right equipment. As Chuckusaret said, it does require dressing around it a bit.
I also will carry OWB sometimes. I find it to be the most comfortable, but don't like that the gun is not held as close to me. I have bumped it off of doorframes, chairs, etc while moving about, especially in confined areas or crowded rooms. Its usually a bit harder to conceal, especailly w/o a jacket.