Big 12 is the stronger conference...no debate necessary.
In the years 2000, 2001, 2003, 2004, 2005, 2008, and 2009 saw a Big 12 team in the BCS title game. The PAC-10 saw three trips in the same span. One of USC's titles isn't without reading about Reggie Bush. The SEC had six berths compared to the Big 12's seven berths.
You obviously value the top of the conference over the competitiveness and depth of the entire conference. Not saying that's wrong. But it does leave a lot of room for debate. Your stats just show that the Big 12 has a few elite programs in Oklahoma, Nebraska and Texas.
With the Pac-12, you've got Cal that hasn't made a top bowl since the 50s. But only 3 other programs haven't made a BCS bowl game since 2000. And all of them did it in the 90s.
Arizona - 1994 Fiesta Bowl
Arizona State - 1997 Rose Bowl
Cal - [not since the 1950s]
Colorado - 2002 Fiesta Bowl
Oregon - 2002 Fiesta Bowl, 2010 Rose Bowl, 2011 BCS Championship
Oregon State - 2001 Fiesta Bowl
Stanford - 2000 Rose Bowl, 2011 Orange Bowl
UCLA - 1998 Rose Bowl
USC - 2003 & 2005 Orange Bowl, 2004, 2006, 2007, 2008 & 2009 Rose Bowl
Utah - 2005 Fiesta Bowl, 2009 Sugar Bowl
Washington - 2001 Rose Bowl
Washington State - 2003 Rose Bowl
In the Big 12, you've got programs like Baylor, Iowa State, Missouri, Oklahoma State and Texas Tech that have never played in one.