Historically AF has a "better" outlook for family, has cushier postings, shorter deployments, better assignments.
That said, I'm just a recently commissioned officer so I have no actual experience in the service and can offer little in terms of comparison. My buddies who are prior service Army will say that AF has nicer bases and postings. Another guy I know said that he really liked his family life while in the AF (had 4 kids) but he also has really liked the family life aspect in the Navy (currently an OS in the Navy, and before D-School did AF as enlist).
Overall, it's also what is easier to get for the 4-year (or 3-year as was my case because I didn't clue into the HPSP until too late). Army and Navy are typically less competitive for 4-year than AF, but then for 3-year, AF has more slots so it's "less competitive". That said, all are very competitive.
Hope the above makes sense.