Here are the top 4 teams from both conferences (by Sagarin) the past 3 years:
2018 PAC: #9 UW, #21 WSU, #23 Utah, #24 Stanford (average: 19.25)
2018 B12: #5 OU, #16 WVU, #17 Texas, #31 OSU (average: 17.25)
2017 PAC: #9 UW, #14 Stanford, #15 USC, #34 Utah (average: 18)
2017 B12: #6 OU, #11 OSU, #12 TCU, #27 Texas (average: 14)
2016 PAC: #4 UW, #10 USC, #18 Stanford, #26 CU (average: 14.5)
2016 B12: #6 OU, #11 OSU, #16 KSU, #28 WVU (average: 15.25)
Looks pretty equivalent to me, at least at the top. Big 12 is slightly ahead (about 2 spots on average per year), but not dramatically.