AAC has more teams that can compete for a playoff spot.
Let's face it, in most years Cal, ORST, Wazzu, Arizona, Colorado, maybe even Stanford (sans Andrew Luck) are not going to be top 20 teams. And it's not entirely clear what will happen to the U of U when KWhitt is done. They might become another meh PAC 12 team. The AAC is gaining momentum, the PAC12 is not.