When choosing your aperture for a portrait photograph, you've gotta ask yourself one major question: "How important is the background - or everything going on around the subject of your photo to you?"
You'll notice in this photo here of Haley, the background wasn't important, it was busy, it was green, it wasn't part of the story. I used a shallow aperture 2.8, for 5.6. That is, the big hole in the lens, to get that nice soft focus on the background while sticking to all this detail here on Haley.
A lot of photographers will select perhaps an F8, at this point, an aperture of 8, which will allow of a lot of the background in, but not completely, and just provide a little bit more ambiance and story in the photograph. So depending on whether or not the background is important to you, and whether or not it's is important to the story, select your aperture accordingly. Remember, the shallower the aperture, the bigger the hole, the blurrier the background will become.