This is in order of importance to the teams' success, how the players in these positions can influence games during the knockout stages of the tournament.
They're too one-dimensional and I don't get excited looking at their back row unit. CJ Stander carries well but doesn't step or do much damage. Peter O'Mahony brings leadership but has been quiet while Josh van der Flier is a level below the very best. Injuries to the likes of Sean O'Brien, Dan Leavy, Jordi Murphy and Jack Conan have limited Joe Schmidt's options and the team are paying for it.
I think France's backs have bailed out their forwards so far in this tournament. Charles Ollivon at openside deserves a pass because he has been good but the others in the back row have failed to step up - and I think England would have made them look very average if they had played last weekend. Wales will be licking their lips at facing them on Sunday.
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Four years ago the 'Pooper' combination of David Pocock and Michael Hooper were unstoppable. They caused havoc at the breakdown but since then everyone else has caught up, with England's two 'fetchers' - Curry and Underhill - likely to fancy their chances on Saturday. Pocock hasn't looked 100 per cent fit and while Hooper has impressed they aren't what they were. I'm not fully convinced by No 8 Isi Naisarani, either.
5. South Africa
No-one can match them for physicality and strength, with Duane Vermeuelen at No 8 one of the most physically imposing players in the competition. Pieter-Steph du Toit has been exceptional, particularly with his work-rate but Siya Kolisi hasn't hit the heights. What concerns me is their slight lack of mobility, and if they come up against a more agile back row, such as Wales in a possible semi-final, they could be found wanting.
4. New Zealand
Ardie Savea is a fabulous player and one of the best ball-carriers around. He'd walk into pretty much any side but I'm not convinced by his two partners in the back row. Sam Cane is brilliant over the ball but doesn't do enough in the loose for me and he hasn't filled that fabled No 7 shirt yet. Kieran Read is a fine leader but I think his performances have dipped in the last 18 months. They're good - but not as good as they were.
I'm picking England in third because of what I think they are capable of, rather than what we have seen in this tournament so far - they really haven't been at their best yet. I'm a big fan of the Tom Curry-Sam Underhill 'Kamikaze Kids' duo on the flank and if Billy Vunipola is fit and firing they can take on anyone. The issue is that Billy hasn't looked anywhere near top form yet. Eddie Jones must be hoping he still has another level or two to go.
They've been fantastic. Michael Leitch was dropped for the game against Ireland but seems to be back to his best, while Lappies Labuschagne is a machine. The man who has impressed me most though is the No 8, Kazuki Himeno. He's added bite, aggression and attitude to this side and has been one of the players of the tournament. The three of them are all leaders within that side and they will relish taking on the Springboks.
Warren Gatland has wonderful depth and a variety of options in his back row, and crucially all his players seem to be in form. What sets them apart for me is the pace and tempo the likes of Josh Navidi, Justin Tipuric and Aaron Wainwright can bring to a game, with the latter coming of age in this tournament. When you consider this is all being done without the injured Taulupe Faletau, who we all assumed would be a huge loss, it is extremely impressive.