The 1971, 1972, 1973, and 1978 teams played VERY tough schedules.
We'll toss out 1970 and 1976 right off the bat.
1971 - absolutely smashed ten-win Ole Miss and whipped ten-win Tennessee. Other than the opener at USC and the win AT 9-3 LSU (both by 7 points) and 9-win Houston (14), this team did not play a single regular season game that ended closer than 16 points. They won their first four post-USC games by an AVERAGE of THIRTY-SIX points. The drilled undefeated Auburn - with Heisman winner Pat Sullivan - by 24 points.
This would be the easy winner.
Well........but then there was a certain bowl game against Nebraska.....
1972 - Tore through the schedule to a 10-0 record with only one close game - the sensational comeback against Tennessee (for those who don't know, we trailed 10-3 for 58 minutes, tied it, then forced a quick turnover and got a quick TD).
But nobody remembers it. Other than the final score was further apart, this year was a LOT like 2013.
Mention 1972 and everyone remembers the Iron Bowl. It's sad because that team deserves better.
1973 - not a single close game, only Tennessee exceeded 14 points until the Sugar Bowl.
Schedule slightly softer - but that's because Auburn (who was 10-0 in 71 and 9-1 in 72) was 6-6 and Ole Miss rotated off the schedule. It wasn't anything we did, as we played Cal, Va Tech (no good then), and Miami.
The other teams did not play overly challenging schedules. We would lose to the one team we should beat.
1974 - not quite as dominant, lost to Notre Dame, trailed for 59 minutes before making it close
1975 - didn't play a single regular season foe with over seven wins and those two were Vandy and USM. Lost to 6-5 Mizzou, rule them out.
1977 - a pretty good team but not an overly taxing schedule.
Looking it over, I think 1978 wins it in a close one for the following reasons:
1) It won the national championship (always important).
2) It won the SEC championship, the seventh in the decade
3) The schedule was nothing short of grueling. Here was September
Nebraska at home
Mizzou on the road (went 8-4 and won the Tangerine Bowl, Kellen Winslow on this team)
USC at home (LOST)
Vandy at home (finally a breather)
Washington on the road (7-4)
Also, MSU was a 6-5 team that year (they were pretty good from 1973-1981) and LSU was 6-1 and ranked number ten when we played them and blew them out on ABC at home.
We then - for some reason - had TWO WEEKS in a row off and then beat a pretty good Auburn team.
And then we beat number one Penn State.
This decade is more difficult than some, but I go with 1978. While the 1979 team was the sole unbeaten through the year, it also played BY FAR the easiest schedule of the 1970s. Only Baylor, Tennessee, LSU and Auburn had winning records - and LSU won only 7 games yet we only beat them 3-0. Yes, we beat Arkansas, but they weren't very good for a 10-2 team.
So I go with 1978.