It wasn't just 1966 with split national champions.
1970 had Nebraska and Texas.
1973 had USC and Alabama.
1974 had Oklahoma and USC.
1978 had USC and Alabama.
1990 had Colorado and Georgia Tech.
1991 had Miami and Washington.
1997 had Nebraska and Michigan.
I'll only discuss the ones about which I think I have some knowledge.
2015 Alabama vs 1969 Texas. Alabama was very strong, beating every team during prior to the CFP championship by a more than a TD. And all of its FBS opponents had winning records. (There was also a blowout win over FCS Charleston Southern.)
Texas looked unbeatable for 9 games, in which they only played one team (OU) that finished the season with a winning record, then had to mount late-4th-quarter comebacks against #2 Arkansas in the season finale and against Notre Dame in the Cotton Bowl. I can't remember if there was some late-season injury that might have been responsible for the offensive downturn, or if it was just the case that they were playing good teams for the first time.
Tough call, but edge to Bama
2000 Oklahoma vs 1980 Georgia. Oklahoma looked like the dominant team in the country through the middle of the season, with a blowout win over a very good Texas team, a 10-point win over a very good K-State team, and a come-from-behind blowout win over a very good Nebraska team. But then nearly every game the rest of the way was a grinder, including a comeback over Texas A&M, a 5-point win over a bad oSu team and a 3-point win over K-State (again) in the CCG. The MNC-game win over FSU was a defensive struggle in which OU won the turnover battle.
Georgia struggled early in the season, with a 1-point win over mediocre-at-best Tennessee in the 1st game and a 4-point win over mediocre Clemson in the 3rd. From that point, the Dawgs cruised for much of the rest of the season, struggling to win by 3 points over USC-E and 5 points over Florida in the WLOCP. The Sugar Bowl game with Notre Dame was a solid 17-10 win.
I'd give mid-season Oklahoma the edge but would favor end-of-season Georgia.
2014 Ohio St vs 1970 Texas. The 2014 Ohio State University Buckeyes were an offensive juggernaut that gave up a lot of points in some of their games. I'm sure that we would see lots of hilarious comments directed at that team had they been playing in the Big 12. However, they only lost once, by 14 points to a mediocre Va. Tech team in the 2nd game, and the only close game they had the rest of the way (which included a blowout over Wisconsin in the CCG) was a 7-point win over Alabama in the CFP Semifinal. The 42-20 win over Oregon in the NCG left no doubt that the Buckeyes were the best in all the land.
IMO, 1970 Texas was a better team than the '69 squad. 4 opponents prior to the regular-season finale finished with winning records, and Texas was only really challenged by one of them, at UCLA, in the 3rd game. There was a blowout win over Oklahoma (which had just installed the wishbone during the bye week before the RRS) and a blowout win over Arkansas in the 10th game. Notre Dame beat the Horns 24-11 in the Cotton Bowl, a game that seems, like an aberration compared to the rest of the season. This opened the door for Nebraska to win the AP (post-bowl final poll) half of the MNC.
Both teams were shaky early and dominant late. Except for Texas in its bowl game. TOSU's loss was in the 2nd game and Texas' was in the last one. If you're playing the teams as they were at the end of the year, advantage Buckeyes.
2006 Florida vs 1974 Oklahoma. The 2006 Florida Gators celebrated the 100th anniversary of the program and the 10th anniversary of their 1st MNC season. Facing the top-ranked schedule in all the land, they mixed blowout wins over weak teams with solid wins and cliffhangers over good and very good teams. The only blemish was a 10-point loss at Auburn (finished 11-2) right in the middle. The 41-14 win over Ohio State in the BCS NCG was a dominant way to finish the season.
The on-probation 1974 Oklahoma Sooners were given the late-season label of "the best team you never saw" by Sports Illustrated. They entered the season on an 18-game unbeaten streak (marred by a 7-7 tie at USC in the 2nd game of the '73 season). The wishbone offense was the best of the three seasons (1973-75) QB'd by Steve Davis. They played a so-so schedule, and were only threatened once, by Texas in the RRS, a 16-13 Sooner win. They beat Nebraska 28-14 in Lincoln, then blew out oSu in Stillwater 44-13 to close out the season. They stayed home through bowl season thanks to the probation.
A tough call.
1996 Florida vs 1985 Oklahoma. Steve Spurrier had the Gators flying with the passing of Danny Wuerffel and the receiving of Ike Hilliard, Reidel Anthony, and Jaquez Green. They also had a new DC who would turn out to be pretty good HFC in his own right. Through 10 games, the closest thing they had to a squeaker was a 28-20 win over Vandy, who, with the benefit of a strip-six of Wuerffel rallied from a 21-3 halftime deficit and 28-6 3rd-quarter deficit to make it close. Then, in the season finale, in a rough game in which FSU was called twice for roughing the passer (and arguably could have been called for the same several more times), Wuerffel was sacked 6 times and there 3 picks. FSU rallied late from a 24-14 deficit, but couldn't come all the way back in a 24-21 loss. Despite a dominating win over Alabama in the SEC CCG, Florida's hopes for a national championship looked dim. But other games broke right for the Gators. Texas beat Nebraska in the inaugural Big 12 CCG. TOSU beat ASU in the Rose Bowl. So Florida would play in the Sugar Bowl for the MNC. Against FSU. Spurrier made some offensive adjustments, Wuerffel threw 3 TDs and ran for another one, and the Gators blew out the Noles 52-20 for their first national championship.
From 1985 through 1987, Oklahoma went 33-3. The three losses were to Miami. That unhappy string started with the 4th game of the 1985 season. OU had a dominant defense led by LB Brian Bosworth, NG Tony Casillas, and DE Kevin Murphy, and the offense was led by promising sophomore QB Troy Aikman operating an I-formation offense. After a 13-7 win at Minnesota, a blowout win over Kansas State, and a 14-7 win over Texas in the RRS, the Sooners hosted Miami. The Hurricane defense knocked Aikman out of the game (and the season) with a broken ankle, and won the game 27-14. The Sooners, back to the wishbone with freshman QB Jamelle Holieway, went on a rampage over the rest of the season, outscoring the next six opponents 229-33. After a 35-13 win over SMU to close out the season, OU beat #1 Penn State 25-10 in the Orange Bowl for the Natty.
Pass defense was the '85 Sooners' Achilles heel, so I'd give the edge to the Gators and Danny Wuerffel in a relatively close, medium-to-high-scoring game.
2013 Florida St vs 1970 Nebraska. This was one of the great FSU teams, led by QB Jameis Winston, dominating the ACC, blowing out rival Florida in Gainesville, and blowing out Duke in the ACC CCG. The only tough game was vs. #2 Auburn in the Rose Bowl BCS NCG. But, after trailing at halftime 21-10, and after three quarters 21-13, the Noles came back to score a TD with 7 seconds and win that one 34-31. The CFB world thanked them for preventing yet another tedious off-season of fans from SEC schools that went 4-8 boasting of their conference's prowess.
The 1970 Huskers were a year away from being one of the all-time great teams in CFB history. This year, they were just very, very good. They tied USC 21-21 in Los Angeles in the 2nd game, then more or less dominated all their opponents the rest of the way. The closest game was a 28-21 win over Oklahoma in Lincoln in the last game of the regular season. Because of the tie, they would not have been national champs except for UPI national champs Texas losing in the earlyish Cotton Bowl on New Year's Day. This set up Nebraska in position to win the AP half of the championship, which they did with a 17-12 victory over LSU in the Orange Bowl.
I'd give the edge to FSU in this one.
2005 Texas vs 1975 Oklahoma. Mack Brown's best team, maybe Texas' best team ever, a team that--in a marvelously thrilling Rose Bowl--beat a bunch of USC Trojans that media-types were calling the best-ever, vs. OU's weakest-ever NC team, a team that wouldn't have even been playing for the MNC had not several other, earlier bowl games broken just the way they did, eliminating better teams than the '75 Sooners from consideration.
Easy--edge to the Horns.
2012 Alabama vs 1971 Nebraska. Alabama dominated its first eight opponents 325-65. Then won a 21-17 squeaker in Baton Rouge. Then got beaten by Johnny Effing Football 29-24 in Tuscaloosa. Then dominated the rest of the way, finishing with a 42-14 blowout win over Notre Dame in the BCS NCG. What to make of that?
The 1971 Nebraska Cornhuskers are at least the 2nd-best Nebraska team of my lifetime, and one of the strongest defenses ever. In Norman, in the real Game of the Century, the real Greatest Game of All Time, they beat the Sooners 35-31, then played a tune-up game at Hawaii, then blew out SEC-champ Alabama 38-6 in the Sugar Bowl.
Edge to Nebraska.