Don't want to be the voice of dissent, but I have been shooting M4s at work for years while on active duty and have even served as the armorer. I have never heard of or seen someone breaking pins who was doing what they were supposed to be doing with the rifle. Normal operation using expected ammunition simply doesn't break pins. I imagine that if this has happened to you more than once, then your rifle is either of shoddy craftsmanship or is experiencing stress that is not normally expected.
But for the question at hand, I would almost certainly choose the AR platform if for no other reason than I am a patriotic American. Choosing the AK for anything seems blasphemous. (the fact that the AK is a foreign weapon could also have something to do with the lower part availability in the U.S.)
