Choosing a captain is always an important decision as a head coach.

Captains are the conduit for a coach's philosophy, a sounding board, an intermediary between the coaching staff and players. They are the rallying point. They set the tone on and off the pitch.

When you go about choosing one, ultimately the most important thing is it is someone who has the respect of his peers; not only from within his team but among the opposition, too. Look at Martin Johnson, Richie McCaw, Paul O'Connell.

On the field, the great ones know almost instinctively when to stand up and influence the game, when to speed it up, when to slow it down, when to secure the ball. Rugby is about momentum and a great captain can give you that.

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I did not have many dealings with Sam Warburton. Obviously I came across him during the Lions tour in Australia in 2013. He was just 24, and injured for the first part of the tour. As he admitted later, he leant on senior players, such as O'Connell and Brian O'Driscoll, to set the tone in those first weeks.

His performances when he did return, though, particularly in the second test, when he was again injured, were an indication of just how good a player he can be.

What I do know is that Warren Gatland clearly thinks highly of him, as do his fellow professionals. So he fulfils that part of the criteria.

His form has been a bit up and down in recent seasons, though. He has struggled with injuries and has struggled to affect the game in the way he did in his pomp.

I think it is a sensible move from Rob Howley and from Warburton himself to take a step back; to try to relax a bit more and just play rugby.

In Alun Wyn Jones, Wales have a natural leader in the Johnson mould.

I always like the option of a captain from the front five. You could see the impact someone like Martin had, not only on his own team-mates but the opposition too; big, strong, taking the fight to the opposition.

Alun Wyn should give Warburton the space to find his game again. It could be very effective for Wales.

In fact, the leadership dynamic heading into this Six Nations is very interesting. Because, although a captain is, as I have said, the talisman, ultimately what all the best teams have in common is a strong leadership group.

What you are looking for, ideally, is a core group of leaders who can take responsibility for different areas. And I mean that literally in terms of areas of the pitch; forwards and backs. And also areas of the game: the set-piece, defence, kicking and so on.

You look at England's 2003 team and - for all that Johnson was the driving force and undoubted authority - there were leaders all through: Lawrence Dallaglio, Matt Dawson, Jonny Wilkinson. Players who took responsibility.

Going further back, looking at the Scotland team of 1990 and the 1991 World Cup, it was the same thing. When Finlay Calder stepped back after the Lions Tour of 1989, he became a good No 2 to David Sole. We had the Hastings brothers, Craig Chalmers, John Jeffrey.

Wales are in a state of flux, trying to find their game. They have one or two leaders but not that many.

Gethin Jenkins is still important. Jamie Roberts can be a leader but his form was not great towards the end of last year.

Having Alun Wyn as captain could just free up Warburton to become a rampaging presence again and Wales will have rediscovered a player who can, on his day, drive them forward. Momentum then grows with these good players feeding off each other.

England and Ireland are in the strongest positions of the six teams in terms of leadership. I would also add Scotland as their game is developing through a strong group of players who are taking more responsibility for their actions. That's why Scotland cannot be ignored.

Ireland's group has formed almost organically, and ironically it has happened just as the vacuum created by the departures of two huge leaders in O'Connell and O'Driscoll was making Irish fans anxious about the future. Conor Murray is playing out of his skin now, Jonathan Sexton has been doing that for ages, ditto Jamie Heaslip, Rob Kearney and captain Rory Best.

For England, you have Dylan Hartley, James Haskell, Chris Robshaw, Ben Youngs and Owen Farrell, who I think is developing into a key player.

I am fascinated to see how Maro Itoje gets on in his second international season now that teams know what to expect from him. He could turn into a very effective leader in time.

Although some feel Hartley should be stripped of the England captaincy, for me, that would be a mistake. As I said, the captain sets the tone. Hartley does that.

He was head and shoulders above the other candidates for England 12 months ago when Eddie was weighing up who to appoint.

In fact, Hartley is still in the frame to be Lions captain. He has made one mistake in the past 12 months and will be hugely disappointed with himself. But overall he was a revelation in 2016 and if he can continue to strike the right balance, he is a very effective leader.

Obviously, I am at arm's length and I am not sure how he is seen by players from the other nations - we are back to my first point about captains commanding respect from all their peers - but that is something Warren must find out from speaking with other coaches.

Warren has some big calls to make. But Hartley and Warburton have to be in the mix.