I'm a 2009 USMMA grad myself going through Primary now.
To answer your questions as best I can, I'd say USNA is harder to get into. I will say, however, that you have a better chance of getting a a pilot slot straight out of USMMA than Annapolis. In my graduating class of 193, we had 3 CG flight slots for 12 applicants, 15 or so Navy out of 20 applicants (the remaining went NFO, not sure of exact number on this one.) We also went 1 for 3 on AF and 2 for 2 for Marines, a small truckload of Army folks (last count I had 12 though lost touch with some folks). I don't pretend to have an intimate knowledge of USNA or any other Academy but I'd guess they're trying to fit a lot more folks through a comparatively much smaller pipe.
Most folks don't go active duty- rumor has it my year was a record year for most branches and less than half the class went active IIRC. That said, the overwhelming majority of people who wanted a pilot slot got one. Hope this helps.