Well, once the kids came our photography shifted rather dramatically to people shots, including portraits. Some of my favorites include a magnificent B&W portrait that my wife Kelly took of me playing piano; I'm biased but it's a wonderful shot. (Some day I need to dig up that negative and scan it.) I have a decent color portrait of Kelly looking over her shoulder that is one of the best I've taken; but when you have a magnificent subject it's tough to get a bad picture. (grin) We have displayed various photos of the kids - some artistic and others not so much. Kelly made a large aperture head shot of our daughter as a baby belly down on the floor that's very nice. I caught our youngest running in the house, hair flying and a look of absolute glee on his face; it captured the spirit of the imp even though it was just a grab shot. As I think on it, the people shots we hang on the walls are the ones that captured the spirit of the subject at that point in time. Not all are 20x30's by the way. We don't have that much open wall space!
Before kids (and marriage) I would put up favorite landscape and architectural photos; I've dabbled in wildlife photography but so far none of that has been hung in the house. My brother-in-law has a number of B&W shots from their travels in Europe hung throughout their house, so we aren't alone in our family in putting up our photos.