Matchup predictor on ESPN has USC as 61.2% to win
TCU at 53.9%

So between those two, the better bet is probably USC, but not by much. But the odds of both USC and TCU winning is 33%.

If OSU gets in with a loss by either favorite, at least according to the odds, there is a higher chance of OSU making it than randomly picking either USC or TCU.

Or what do I know, I probably did this wrong because I suck at math.

I would probably pick USC. I also didn't do any math on alternate options that would get teams in besides simply winning this weekend.