While it won't get a lot of support, I think the best team of all-time that never lost a game (certainly in my lifetime) was the 1991 Washington Huskies. If you get a chance to locate some of their games,watch them. They are so much like the 2011 Crimson Tide on both sides of the ball that it is absolutely frightening. An absolutely awesome defense, two backs - one big power back and a small runner (their version of Lacy and Yeldon), an incredible O-line. They also had a two-headed QB of Mark Brunell and Billy Joe Hoebert (AJ was obviously not as great in 11 as he became).
They not only beat everybody - they mauled all except one team. They drilled an 8-4 Stanford in Palo Alto (coached by former 49er head coach Bill Walsh), went into Nebraska and overcame a 21-9 third quarter deficit to pound the Huskers, 36-21. And don't let the score fool you. One of Nebraska's three TDs was caused by a punt fumble at the Huskies own three-yard line early in the second half. It's almost like Nebraska scored to put up a gap and it made Washington REALLY mad.
Their only close game was on the road in Berkley at 10-2 Cal, where they won by a TD. There are only TWO teams in the modern era that were unbeaten and had only one opponent within a score of them at the end: 1995 Nebraska and 1991 Washington. A lot of pundits think 95 Nebraska was the best ever but I'll note that Washington played a bit tougher schedule (if we're going to have that argument).
And btw - the 1990 version of this team probably should have been national champions. Yes, they lost two games, but remember that Colorado had a loss and a tie that year. And yes, Colorado beat the Huskies at home, 20-14, but if you've seen this actual game it's a lot like 2011 Alabama-LSU in Tuscaloosa in the sense that the team that generally played better lost. Washington was victimized both by a bad officiating call (that wouldn't happen today most likely), two key injuries to both receivers on the final drive (they actually had first and goal with a shot to win), one receiver falling down on the wet turf wide open in the end zone, and just a theatre of the bizarre. The 90 team was not the best of all-time but may have been one of those cases where the "best team this year" did not win the title.
However, there's a lot of debate on this. I cannot really say that 95 Nebraska or 01 Miami - both outstanding teams - were not better. But I can say this for certainty: losing to Houston Nutt at home pretty much rules out Urban's opinion from any form of reality.
I do, however, think part of this is a product of the fact most of us (self included) don't tend to stay up and watch most West Coast games. It was much harder back then because there was no Net, no ESPN2, and prime time on ABC or CBS almost never happened. Fewer games = fewer chances to see.
Anyway, that's my view.