Rugby's World XV is subject of constant debate among fans, but we become more preoccupied every four years as selection in the team that never plays is seen to provide a strong guide to the merits of the leading Rugby World Cup contenders; the more players selected the better your cup credentials, obviously, but it is said often that a team must have at least four walk-up World XV starters to be a contender.

We've decided this year to approach the discussion from a different angle; rather than selecting a World XV, we're listing four players in each position, irrespective of nationality, in order to gauge the absolute depth of the respective cup candidates. (We have listed eight wingers and eight locks rather than specifying left and right.) The current list has been selected according to form in the past six months.

Of course, you might disagree with a number of the selection - or all of them if you are being totally contrary. And that's OK because we encourage - and hope to enjoy - vigorous debate.

We'll update the list each four weeks, according to form displayed in the Six Nations, Super Rugby, European club competition, the Rugby Championship and, closer to Rugby World Cup 2015, the final warm-up matches; we hope the lists will provide a gauge to the absolute strength of the contenders and, more importantly, a vibrant discussion - both about the players we have selected and omitted, and about the legitimacy of the various RWC campaigns.

And, so to the initial list.

Willie le Roux: is he the best full-back in world rugby? © Getty Images

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Full-backs

Israel Dagg (NZL), Israel Folau (Aus), Leigh Halfpenny (Wal), Willie Le Roux (RSA)

Wingers

Tommy Bowe (Ire), Niki Goneva (Fij), Bryan Habana (RSA), Cory Jane (NZL), Nemani Nadolo (Fij), George North (Wal), Julian Savea (NZL), Ben Smith (NZL)

Outside Centres

Adam Ashley-Cooper (Aus), Wesley Fofana (Fra), Tevita Kuridrani (Aus), Conrad Smith (NZL)

Inside Centres

Jean de Villiers (RSA), Ma'a Nonu (NZL), Jamie Roberts (Wal), Matt Toomua (Aus)

Jonny Sexton is th3 only non-All Blacks player among the initial four fly-halves © Getty Images

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Fly-halves

Beauden Barrett (NZL), Dan Carter (NZL), Aaron Cruden (NZL), Jonny Sexton (Ire)

Scrum-halves

Conor Murray (Ire), Ruan Pienaar (RSA), Nick Phipps (Aus), Aaron Smith (NZL)

No. 8s

Samu Manoa (USA), Sergio Parisse (Ita), Kieran Read (NZL), Duane Vermeulen (RSA)

Opensides

Michael Hooper (Aus), Francois Louw (RSA), Richie McCaw (NZL), Chris Robshaw (Eng)

Blindsides

Willem Alberts (RSA), Jerome Kaino (NZL), Liam Messam (NZL), Peter O'Mahony (Ire)

Locks

Eben Etzebeth (RSA), Alun-Wyn Jones (Wal), Courtney Lawes (Eng), Victor Matfield (RSA), Paul O'Connell (Ire), Brodie Retallick (NZL), Sam Whitelock (NZL).

Agustin Creevy features among four Pumas in the initial list of front-rowers © Getty Images

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Tight-heads

Juan Figallo (Arg), Owen Franks (NZL), Ramiro Herrera (Arg), Nicolas Mas (Fra).

Hookers

Dane Coles (NZL), Agustin Creevy (Arg), Bismarck du Plessis (RSA), Adriaan Strauss (RSA).

Loose-heads

Marcos Ayerza (Arg), Cian Healy (Ire), Joe Marler (Eng), James Slipper (Aus).

Teams represented: Argentina 4, Australia 7, England 3, Fiji 2, France 2, Ireland 6, Italy 1, New Zealand 17, South Africa 11, United States 1, Wales 4

Who should be here? Who shouldn't be here? Who do you think will move in and out of the list before England and Fiji kick-off Rugby World Cup at Twickenham on September 18? Join the debate in the comments fields below, or on Twitter using the hashtag #RWCDepthChart. We look forward to hearing from you.

Chris Robshaw is gaining increasing admiration as an openside © Getty Images

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Aaron Smith is one of 17 All Blacks in the initial list © Getty Images

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