I think it is legitimately a really close call between tOSU and Michigan for the top spot. Here are their results sorted by Sagrin ranking for their opponents:

Michigan's big win over Penn State stands out as easily the most impressive result by either team but their 13 and 7 point wins over Iowa and Maryland stand out the other way. Ohio State seems to be a bit more consistent with nothing really jumping off the page in a good or a bad way relative to Michigan.
As an Ohio State fan, Michigan looks scary to me. I don't mean scary just to lesser teams, I mean scary to the Buckeyes as well. When they are good, the Wolverines are REALLY good. Here are Indiana's second half possessions against the Wolverine defense:
- 7 plays, 26 yards, punt
- 3 plays, 7 yards, punt
- 6 plays, 23 yards, punt
- 3 plays, -9 yards, punt
- 3 plays, -11 yards, fumble
- 6 plays, 8 yards, downs
That would be impressive against an FCS opponent, it is REALLY good.
Here are Penn State's four possessions after they kicked a FG to take a second-half lead:
- 9 plays, 36 yards, downs (while down 24-17)
- 5 plays, 16 yards, punt (while down 31-17)
- 6 plays, 22 yards, downs (while down 34-17)
- 9 plays, 42 yards, downs (while down 41-17)
While their defense was doing that to the PSU offense, the Michigan offense scored on four straight drives (3 TD's, 1 FG) to turn a 17-16 PSU lead into a 41-17 Michigan blowout.
Like I said, when they are good they are REALLY good. That said, they also have a trend of letting inferior teams hang around. Indiana was tied at the half and within one score until midway through the final quarter. Penn State, despite getting statistically obliterated, was only down two at halftime and very briefly held a second half lead. Maryland was within four at the half and within one score for all but a few minutes. If they keep playing questionable first halves it is likely that one of the teams they should beat will knock them off and/or that Ohio State will build up such a massive lead that the Wolverines will be unable to catch up.