CFP Championship Game:

From Sports Media Watch

2015: Ohio State/Oregon, 18.6, 34.15M
2016: Alabama/Clemson, 15.0, 26.182M
2017: Clemson/Alabama, 14.2, 25.266M
2018: Alabama/Georgia, 15.6, 28.443M
2019: Clemson/Alabama, 13.8, 25.280M
2020: LSU/Clemson, 14.3, 25.59M

With Alabama the common denominator, Georgia had a higher viewership than the three Clemson games by over two million viewers over any of the three of the games. With Clemson the common denominator, LSU and Alabama didn't seem to make much of a difference.

The (January) 2015 game was the first game and probably got more viewers than expected. I'm sure Ohio State also helped as well (can't believe Oregon was worth anything). On paper, Ohio State would be better than Clemson or Georgia with Alabama as the common denominator. But COVID-19 will depress the viewership for sure. I'm guessing the viewership will be pretty similar to the last two years, around 25 million. If this was a non COVID-19 year, I'd go more for the 2018 year, 28 million. The other significance about 2018 is that in 2018 the semifinals were on New Year's Day and the semifinals draw more viewers when they are on New Year's Day vs. when they are not and that was the case this year although again this year was a COVID-19 year.