One of the many joys of sport is its role as conversation fodder. I spotted an article the other day in which a journalist mentioned that he and colleagues had been asked what their starting line-up would be from a combined Chelsea and Manchester United squad.

I never got to the end of the article but a good hour-long chat with my sons later, we settled on Petr Cech in goal, Gary Neville, Rio Ferdinand, John Terry and Gabriel Heinze in defence, Cristiano Ronaldo, Frank Lampard, Claude Makelele and Arjen Robben in midfield, with an all Red Ruud van Nistelrooy and Wayne Rooney up front. So six United and just five Chelsea.

And as Chelsea chief executive Peter Kenyon has the occasional sleepless moment questioning the wisdom of his statement that the champions will come from a pool of one, it was interesting to note the United dominance of our agreed bench too - Edwin van der Sar, Mikael Silvestre, Roy Keane, Damien Duff or Ryan Giggs (we couldn't separate and at one point Giggs was in the first XI instead of Robben) with Hernan Crespo the only definite Chelsea choice as a substitute.

For the record, we opted for Roman Abramovich as owner ahead of the Glazer family (a close call) and Alex Ferguson as manager ahead of Jose Mourinho.

So all in all, a good conversation for Manchester United and a nice way to get through the first part of another lazy holiday morning.

It was another such conversation a couple of years ago that led to one of the best journalistic assignments anyone could ever have landed, when I persuaded The Times of London to publish a lengthy series during which I interviewed some of the greatest names in sport, to help me decide who was the greatest of all.

The conclusion - Muhammad Ali - was a bit predictable maybe, but a journey that included interviews with the likes of Lance Armstrong, Haile Gebrselassie, Seb Coe, Hicham el Guerrouj, Gareth Edwards, Ian Botham, Geoff Boycott, Michael Phelps, Nadia Comaneci, Roger Federer, Lleyton Hewitt and Jon Ove Waldner was anything but, for me at least.

Who is Jon Ove Waldner, I hear one or two of you ask.

Let me answer with a question that provides a clue - who is the second-most-recognised Westerner in China (Bill Clinton being the first)? The answer is Waldner, a Swedish table-tennis legend from Stockholm to Shanghai, if not at all points in between.

What I discovered along the way is that part of people's interest in sport is the permission it gives us to hold views, and hold them strongly.

Deciding whether Ali the boxer is a better athlete than Armstrong the cyclist is always going to be a matter of opinion rather than scientific fact.

There can be no result as there is in most sport. And yet there can be as much fun and passion in the discussion as there is in many sporting events.

Likewise, ask yourself whether Coe and El Guerrouj, the middle-distance runners, are better or worse athletes than Carl Lewis the sprinter and long jumper, or Michael Johnson the sublime 200 and 400-metres runner.

There is no definitive answer, yet we can all have our own.

I read another piece at the weekend by former Republic of Ireland and Leeds midfielder Johnny Giles, in which he expressed exasperation that George Best and Eric Cantona so regularly come out as Manchester United's best ever players in polls of fans. In Giles's view, there could be no doubt at all that the greatest Red of all time is Bobby Charlton. You can certainly make that case, as Giles did.

But equally you can see why others would opt for Best or Cantona. Charlton was a great footballer and - still is - a great ambassador for the club and the game. Best and Cantona were flawed but supremely gifted characters whose outsize personalities elevated their status in the eyes of fans way beyond the level to which their phenomenal skills alone would take it. Charlton is a legend primarily on achievement.

The legendary status of Best and Cantona derives as much from their flaws and failings and the passions they arouse as people. It is the same quality that leads most people to name Ali as the greatest sportsman of all time. He was a great boxer, but he fought some bad fights. He was a great man at the height of his powers, but he did some bad things. But above all he was an enormous character who used his sport, his fame and his personality to make the world a different place for many people.

The great characters are the ones that endure, which is why, since starting this article, I have decided to drop Lampard and install Keane as captain. Just as Manchester United fans still sing songs about Cantona, so they will sing about Keane when he's gone. That fact may not be as important as a goal, a pass or a tackle, but it is part of a contribution to sport, and worthy both of conversation and recognition.

It also means Manchester United 7 Chelsea 4. The Premiership title is wide open, Mr Kenyon. Discuss.