The story and the legacy of the Busby Babes is a tale that stretches over more than 50 years, from their triumphs before the tragedy of the Munich Air Disaster in 1958 to United's third major European win in 2008.
In the 20th century, United had three undeniably great teams—two managed by Sir Matt Busby and a third put together by Sir Alex Ferguson.
They were the 1999 treble winners of Keane, Beckham, Giggs and Scholes, the 1968 European Cup winners of Best, Law and Charlton, and, of course, the Busby Babes.
Power ranking such a trio is a difficult assignment, especially considering that most people only have first-hand experience of the most modern of the three teams.
Yet based on the accounts from those who watched them and enjoyed them, we will attempt to gauge the strength of each great side against the other, from the sheer equilibrium of Fergie's comeback kings to Busby's two legendary sides.
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The Holy Trinity immortalised: George Best, Denis Law and Sir Bobby Charlton
Line-up (4-3-3): Alex Stepney; Tony Dunne, Bill Foulkes, David Sadler, Francis Burns; Nobby Stiles, Sir Bobby Charlton, Pat Crerand; George Best, Brian Kidd, Denis Law.
Notable squad players: Shay Brennan, John Aston, John Fitzpatrick.
United's first European champions featured three of the club's most celebrated players.
Denis Law, Sir Bobby Charlton and George Best were known as the Holy Trinity: a fulcrum trio of goals, creative and genius who could win and master games at will.
All three would become Ballon D'or winners and they were the undoubted stars of Sir Matt's second great team in attack, midfield and on the wing respectively.
Though they were certainly a cut above their teammates, the other members of the 1968 squad were great players in their own right.
Alongside Charlton, Stiles was a World Cup winner with England in 1966 and as key for his club and country at the base of midfield as his more illustrious colleague who would one day be knighted.
Stiles was a tough-tackling defensive midfielder and the deep-lying anchorman of his day.
His presence in front of defence allowed Sir Alf Ramsey's 4-4-2 to function on the international scene and added some necessary bite to United's midfield.
Assisting him in dominating the centre of the pitch in Busby's team was Pat Crerand, another combative midfielder who was also a prolific creator of chances for the likes of Law and Best in attack.
They combined well with Charlton, who was undoubtably the side's star playmaker.
Brian Kidd was Law's able partner upfront, but he was far more than a mere deputy, scoring hatfuls of goals himself. In fact, with Law unavailable for the 1968 European Cup final, it was Kidd who carried the burden as the team's main striker against Benfica.
Before Schmeichel, there was Alex Stepney, an equally imposing figure between the sticks, ready to bark orders and discipline his defence when their concentration lapsed.
In front of him played full-backs Dunne and Burns and central defenders Foulkes and Sadler.
Foulkes, along with Busby and Charlton, was a living link back to the Busby Babes. He himself had survived Munich, going on to captain the side through their remaining fixtures in 1958.
Another one of United's notable defenders in 1968 was the young Irish full-back Brennan. He had been recruited by Jimmy Murphy following the disaster and played at right-back in United's 4-1 European triumph, 10 years on from the loss of the Babes.
Winning the European Cup in 1968 was an incredible feat for the club and Sir Matt, considering what had happened a decade earlier.
Not only were the Holy Trinity and their teammates pioneers as the first English winners of the competition but also the players who finished the job started by their predecessors in 1956.
Line-up (4-4-2): Peter Schmeichel; Denis Irwin, Jaap Stam, Ronny Johnsen, Gary Neville; Ryan Giggs, Roy Keane, Paul Scholes, David Beckham; Andy Cole, Dwight Yorke.
Notable squad players: Ole Gunnar Solksjaer, Teddy Sheringham, Nicky Butt, Phil Neville, Jesper Blomqvist, Wes Brown, Henning Berg, Raimond van der Gouw.
Sir Alex's treble winners were in many ways the culmination of the Busby Babes story.
Back in 1958, before the vaunted team were lost on the return flight back from Belgrade, the Babes were in the race to win the First Division, the FA Cup and the European Cup.
The class of 1999 fulfilled what many fans and neutrals of the time believe to be the potential of Busby's prodigies.
While they may have lacked the individuals of the 1968 champions, the treble team remains one of the most perfectly balanced and blended sides of all time, with an indomitable spirit that inspired comeback after comeback.
Giggs, Keane, Scholes and Beckham were a midfield with everything, while Cole and Yorke operated on a level that fit the cliche of a telepathic partnership.
From the bench, Solksjaer and Sheringham would prove to be two of the most decisive super subs ever, while Phil Neville and Nicky Butt offered the utility and tenacity to plug gaps and add some extra backbone as required.
Like the midfield combination, at the back Irwin, Stam, Johnsen and Neville were a harmony of skill, strength, intelligence and awareness, backed up by the Great Dane himself, Peter Schmeichel.
The 1999 team was the footballing equivalent of the planets aligning, with the instant chemistry of their new signings and a commitment to developing Fergie's Fledglings—the Nevilles, Beckham, Scholes, Giggs and Butt—dovetailing into a team that would go on to complete a treble of back-to-back Premier League titles in 2001.
Regardless of their qualities, however, placing them above the Holy Trinity is a big call and one that many will disagree with.
It's not the opinion of a rogue football writer, however, but of Sir Bobby Charlton, who in 1999 told the press, per the Irish Independent:
The team of today is much better prepared than we were in terms of fitness and conditioning. We didn't train with anything like the same intensity as they do now. Though I do believe that, as individuals, the players on the 1968 team would be good enough to play today.'
Inevitably people will make comparisons with the 1968 European Cup winning team and as one of the players then, I can honestly say I have never played in or watched a better United performance.
Fergie's 1999 vintage certainly had staying power and a never-say-die attitude, which—along with their unprecedented treble win—is enough to elevate them as a unit above the 1968 European Cup winners, even if none of their number could match Law, Charlton and Best.
The Busby Babes: the flowers of Manchester.
Line-up (2-3-5): Harry Gregg; Roger Byrne, Bill Foulkes; Duncan Edwards, Mark Jones, Eddie Colman; David Pegg, Liam "Billy" Whelan, Tommy Taylor, Dennis Viollet, Johnny Berry.
Notable squad players: Jackie Blanchflower, Sir Bobby Charlton, Albert Scanlon, Kenny Morgans, Geoff Bent, Ray Wood.
With the teams of 1968 and 1999 coming third and second in our power-ranked order, that makes the Busby Babes No. 1.
If Busby's second team had the greater individuals, and the treble winners were the more complete team, then the Babes were said to be somehow superior to both their successors in both ways.
In Duncan Edwards, they had a player thought to be destined to become one of the very best, while the likes of Taylor, Byrne and Colman were exceptional players in their own right.
Blanchflower, young brother of Tottenham Hotspur great and player-turned-journalist Danny Blanchflower, could add a touch of finesse in place of Jones, who was the Babes' primary enforcer alongside his fellow half-backs Edwards and Colman.
A half-back was a position that has since become obsolete, which worked out as a sort of hybrid of a defensive midfielder and centre-back.
Byrne was the Babes' captain at full-back and one of the most respected defenders of his day, often paired with Foulkes, who would go on to complete his team's European mission in 1968 and take on his friend and mentor's role as leader. Bent was their able and ready back-up.
Full-backs in those days made up a two-man last line of defence, behind which Gregg would tend to the goal.
The Northern Irishman was dubbed the hero of Munich for his bravery in saving others from the crash site, and he was equally courageous and bold on the pitch, demanding others lift their game or inspiring them to do so.
Before the team was lost on the tarmac in Munich, they were competing for three trophies and coming into their own on the international scene.
In 2008 David Meek recounted some contemporary opinions on Duncan, Byrne and Taylor from an England national team colleague, Jimmy Armfield, and manager Walter Winterbottom for The Guardian.
Armfield on the three Babes:
With Duncan Edwards, Roger Byrne and Tommy Taylor in the team, I believe England would have reached the final of the 1958 World Cup, and probably won it. Playing in the same team together I can still see this powerful figure stalking the dressing room and at the time I would think: 'I'm glad he's playing for us.'
Winterbottom on Edwards:
Duncan was a great footballer and he had the promise of being the greatest of his day. He played with tremendous joy and his spirit stimulated the whole England team. It was in the character and spirit of Duncan Edwards that I saw the true revival of British football.
There are some who have questioned whether Bobby Moore would have been such a key figure for his country, let alone captain, had Edwards not been killed, as per The Telegraph.
Sadly, such thinking is entirely academic since the half-back never got the chance to fulfil his promise.
Taylor was the quintessential English No. 9, leading the line while maintaining a prolific goal-scoring record for his club and country. Around him would swarm the likes of Billy Whelan, Dennis Viollet and wingers such as David Pegg, Kenny Morgans, Johnny Berry and Albert Scanlon.
Like Sir Alex's United sides at their best and most fluent, the Babes overcame their opponents through excellent movement, positional fluidity and a fearsome appetite for goals in attack.
The Busby Babes were the team that launched the modern United legend and, according to many of those who watched them and played with them, they haven't been bettered in the club's colours since.
It's easy to forget that going into the 1958 European Cup competition, it was the Babes who were the favourites to win in the eyes of many in Europe, not Real Madrid who were already on their way to completing their historic five-in-a-row clean sweep in the tournament's early years.
While the 1968 team may have taken on their European baton and the 1999 champions completed their full-frontal assault on the trophy cabinet, neither would have needed to undertake such assignments to finish the Babes' work had Sir Matt's first great team survived.