1. New Zealand
It hasn't been totally smooth sailing for the World Champions so far. Their performances have been littered with errors and merely sprinkled with individual moments of magic. In attack they haven't clicked the way one would expect, and against some strong packs they have struggled, but those are the only real problems.
Their defence has been very strong. They are missing very few tackles, the fewest in the tournament in fact, and that will stand them in good stead in the knockout stages. To win the tournament they will need to become more clinical, but that switch could be pulled at any moment.
They are in a rare position of having numerous combinations that all have experience together. Whichever centre pairing they choose, there is chemistry. Their back row can chop and change without diminishing returns and the balance through their whole squad is remarkable.
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It is also worth remembering that this isn't an All Black side that chokes under pressure, or fades away in the face of adversity. They have shown that they can win ugly, and it's likely they will have to do just that at some point. Their leadership core is phenomenal with the likes of Dan Carter, Ma'a Nonu and Ben Smith in the back-line, and Kieran Read and Richie McCaw up front.
They might not have played like the favourites, but until they get beaten, that's how they should always be treated.
As they so often do, the Wallabies seem to be timing their run to perfection. Always strong at World Cup time, Michael Cheika seems to have developed his squad from talented individuals into a cohesive juggernaut.
Mario Ledesma, with some strong personnel, has transformed the scrum from an Achilles Heel into a real weapon. They have one of the biggest packs in the competition but also one of the most athletic. Their props got the better of their opposition significantly in every match of the group stages and that is without the hefty bulk of Will Skelton turning the wheels.
To have that in front of their back-line that is gelling better and better with every match is a daunting prospect.
The Aussies are a hard bunch to beat at the best of times, but they have shown against England and Wales that their current squad may be world beaters. Even down to 13 men against a rabid Wales attack they held out heroically. It will take a very special performance to topple the Green and Gold. New Zealand may be something of an unknown quantity going into the quarters, but you can be sure that the Aussies will be on point.
Their star studded line-up poses threats across the park unlike any other side. With Michael Hooper and David Pocock as a unit they have the most efficient back row in world rugby, and with the likes of Matt Giteau, Adam Ashley-Cooper and Israel Folau causing mayhem in defences they will fear no opponent.
The fact that they are on the opposite side of the draw to New Zealand makes an all Southern Hemisphere final good money at this point. All the evidence of finals gone by suggests that experience beats out flair, and leadership trumps just about every other factor. In that intangible department, New Zealand are head and shoulders above the rest.
The run up to the knockout stages has been a mixed bag for Ireland. Six Nations Champions, then they lost two on the bounce. Clinical wins against Canada and Romania, and then a sloppy performance against Italy. Finally a dominant and consistent outing against France to ensure top place.
If they can replicate that intensity for further 80 minute wars, they will likely win the trophy. But if they let errors start slipping into their strike moves, and begin to doubt themselves then it only takes one slip up to dash their hopes.
With Joe Schmidt at the helm, there is no doubt that this team can win the World Cup. They have strength in depth, a tremendous defence, high level organisation and a very strong spine to their team. In short they have everything they need to get the job done, but it all depends on their consistency.
Injuries have taken their toll, and unfortunately to several true leaders. However, their replacements have shown that in terms of talent, there is minimal drop-off.
If they can get their smothering game to work they might be the best placed side to lift the gold. They have been winning more often than not as of late so the test will be whether or not they can do so on the biggest stage.
4. South Africa
The Springboks made a terrible start to the tournament. They've had one of their worst years ever, in fact. But that seems to have galvanised them as a side and woken a sleeping monster. The way they battered through a confident Scottish side left no one under any illusion what a test it will be to put them away.
Their squad is mixed between players right at the end of their careers, and many right at the start, and a fair few in their absolute prime. The blend hasn't worked on a consistent basis, but there is no doubt that the talent to go far is there on paper.
They have shown a mental frailty in closing out matches in recent times and as the pressure ratchets up this may give other sides an edge. But either way, their physical attributes will largely compensate.
2015 may be too soon for this squad to be champion material, but whoever beats them will either emerge broken, or strong favourites.
Despite coming second, the Pumas were the best performing side in their Pool with the All Blacks. They always come strong into World Cups and their time in the Rugby Championship has clearly paid dividends.
Their strength in the pack is a given but they have truly developed a world class backline with dream team candidates throughout. This has shown in their performances where they have scored some of the competition's best tries with clinical strike moves, and fluid phase play. To beat this side you will need a complete performance.
Their whole team is playing with heads up, and offloading with accuracy. This is made easy by the work off the ball with numbers flooding to support every clean break.
You feel that against sterner defences the champaign skills they have demonstrated so far will be made much more difficult to execute, and perhaps they haven't got the consistent game breakers throughout the spine of their team to win gold.
The collective experiences of Warren Gatland's squad that includes World Cup heartbreak, Six Nations triumphs, and Lions tours has made them an extremely motivated side. Their injuries have been well documented, but their starting XV still looks as strong as most.
The back row is always a key area and they have world class operators throughout. With the depth they have in that area they stand a chance against any team, but you feel they may already be close to their potential.
Where the top teams always have another gear they can move into, Wales seem less likely to reach those heights. As well as tremendous nerve and accuracy they also needed a lot of luck to beat England, and while every team needs some luck to win the World Cup, Wales might not have the tools to go all the way.
Another gutsy performance could see them to the semis, but going further than that is a tall task.
The French are like a box of chocolates. Forrest Gump knows why. In 2011 they became arguably the worst finalists in the history of the competition, and then very nearly beat the best team in the world. They are famous for beating the All Blacks in World Cups, but this is a different French team.
Their trademark French Flair has become rarer and rarer, but their brutal power has undoubtedly increased. Their squad quality has possibly been a detriment as it's hard for individuals and combinations to build momentum, but this also makes them hard to prepare for. If they don't know what they're going to do next, how will the opposition?
Set piece parity is a key to victory against this side. If you let their pack get on top, however, the likes of Wesley Fofana and Mathieu Basteraud will punish you. Other teams are more consistent so I would lean towards an early exit for the French, but who would ever put money on their matches?
When it looked like they might be well placed to top the group, Scotland might have been contenders for shock quarter finalists.
But against South Africa they were exposed for the limitations of their squad. They don't have the power to arm wrestle the big nations, and they don't have the class in their backline to split watertight defences.
Their own defence has looked woeful in their last matches, with South Africa smashing through the gainline all afternoon, and Samoa scoring far too many simple tries without too much done to earn them.
Both their half backs have had outstanding tournaments thus far, pulling the strings and getting the best out of the back division. Mark Bennett and Tommy Seymour have looked very good against lesser competition but against world class units they will need to dig very deep to get the upper hand.
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