Button and Hamilton will go head-to-head with McLaren this season
Motor racing legend Nigel Mansell believes Lewis Hamilton will have the edge over Jenson Button at McLaren when the new Formula 1 season begins.
Hamilton, the 2008 winner, teams up with reigning champion Button in a eagerly anticipated 2010 season.
Mansell told BBC Sport: "I'd give Lewis the edge only because he's been there for a couple of years."
However, Button's former team boss Brawn disagreed, saying: "Jenson has a depth that people do not see."
Brawn added: "He has this fluffy exterior that hides the steel inside him.
"You saw that in the second half of the year [last season]. The first half of the year he was sublime.
"Only one of them can win and how is the other going to cope with it? Two world champions determined to prove that they are the best."
Hamilton has admitted he considered quitting following a much-publicised incident in Melbourne last year when he was persuaded by then-sporting director Dave Ryan to mislead stewards.
But the 25-year-old continued with McLaren and is now gearing up for a new season with Button as his team-mate, following his switch from Brawn.
Mansell, who won his first title at the age of 39 in 1992, added on Radio 5 Live's Sportsweek: "Jenson will settle down and hopefully prove what a great world champion he is and compete very strongly.
"I think they are both number ones in the same team. I give Lewis the edge for the first six races because he knows the team and the people and the car.
"Jenson will take a few races to get up to speed with the car but after that they should have total parity."
Mansell also believes returning former world champion Michael Schumacher is unlikely to add another trophy to his seven-title haul in his first season back in F1 - but did not rule it out in the future.
Schumacher, 41, will take to the grid with Mercedes in the first race of the season in Bahrain next Sunday.
Mansell won his first F1 title at the age of 39 in 1992
Mercedes is run by Brawn, the team leader who guided Button to the world title at the now defunct Brawn team last season and Schumacher's boss in a hugely successful spell with Ferrari.
"In the first year [the world title] probably is a little bit too far but if he's in for a couple of years I don't see any reason why not," Mansell said.
"I certainly put him down for some race wins this year.
"Anything is possible with Ross Brawn and Michael. He's back with his old mentor."
Mansell, now aged 56, even floated the idea of a return to Formula One.
He is currently involved in the Le Mans series driving for Team LNT alongside his son Greg.
But, when asked if he might return, said: "Never say die. If there's a good Formula One seat, who knows? Why not, it would make a bit of history, wouldn't it?"
"We're pulling four to four and a half G in these cars so who says anything can't be done these days? It's about having the opportunity."