As you have seen in this thread, there are valid arguments on both sides. I chose a semi for the capacity. Cops are said to only average a 20% hit rate. We can assume we will be better, but will we? If we don't, that means we will only hit the BG once by unloading the average revolver. Thus, we are forced to assume a one-stop shot and just one BG. I'm not ready to bet my life or the lives of loved ones on those assumptions. And what if the BG gets me and my wife is on her own? She doesn't shoot as often or as well as me, so how many rounds might she need?
I used to carry a revolver. I like revolvers. I switched to semis a while back for self defense. The extra capacity seems to my mind to be a significant advantage. Think it over and reach your own conclusion, though - I'm just explaining my thought process.