New Zealand: Reigning champions

However, the tournament is unlikely to prove an accurate guide as to who will lift the William Webb Ellis trophy in Auckland in October.

The tournament has been truncated for the final edition in its current incarnation - Argentina are set to join in 2012 - with sides only playing each other home and away due to the timing of the World Cup.

South Africa's form ahead of the defence of their world crown is likely to be the most difficult to judge, with coach Peter de Villiers claiming that 21 senior players are carrying injuries.

That has seen an understrength squad selected for their away leg of the competition, taking in the meetings with Australia in Sydney on Saturday and New Zealand in Wellington a week later, and they are likely to open with two defeats.

The omission of such players as wing Bryan Habana, flanker Schalk Burger and lock Victor Matfield has led many, including Australian Rugby Union chief executive John O'Neill, to accuse the Boks of resting their stars ahead of the World Cup.

Whatever the reason, it means the Springboks are likely to repeat last season's showing by finishing bottom of the table, although their form once their stars return for their home fixtures may at least be instructive in terms of the upcoming global showpiece.

Australia have been buoyed by the impressive performances of half-backs Will Genia and Quade Cooper and lock James Horwill as the Reds romped their way to the Super Rugby title, but that confidence has been rapidly sapped by a woeful display in Sunday's shock defeat to Samoa.

But there were plenty of unfamiliar faces in the line-up that faced the South Sea Islanders and, at full strength, Robbie Deans' men are capable of running New Zealand close.

The Wallabies possess arguably the most exciting backline in the game with Genia and Cooper joined by the likes of Kurtley Beale, James O'Connor and Digby Ioane.

They also have a well-balanced back row in the form of skipper Rocky Elsom, David Pocock and Ben McCalman, but the key, as always, will be their scrum.

The set-piece has been a weakness in Australia's game for over a decade, and a knee ligament injury to Benn Robinson is unlikely to help matters as they seek a first Tri Nations title since 2001 and a first Bledisloe Cup triumph since 2003.

All that means that New Zealand are favourites to claim an 11th title as the pressure builds towards pressure-cooker intensity for their hosting of the World Cup.

While it remains to be seen if Graham Henry's side can shake off the tag of being bottlers on the game's biggest stage, they have had few such problems ramming home their dominance outside of the knockout stages of a World Cup.

There have been suggestions that below-par performances from the Super Rugby franchises mean a dip in form for the national side is imminent, but it is worth remembering that the Blues reached the semi-finals, while the Crusaders were beaten finalists.

The All Blacks also showed themselves to have a handy advantage over their rivals in last year's tournament, racking up six wins from six during a 2010 campaign that also saw them complete a crushing Grand Slam in Britain and Ireland.

Key men such as Richie McCaw and Dan Carter are likely to be handed a break at some point given their importance to New Zealand's World Cup hopes, but it is difficult to bet against Henry scooping more silverware from his final Tri Nations assault.