Cape Town - Free State Cheetahs defence coach, Michael Horak, says Argentina have impressed him the most of all the Rugby World Cup quarter-finalists.Click to BUY the new FIFA 12 gameClick to BUY the new Drifta Mobile USB DecoderHorak - also a former England fullback - says Argentina's strong defence makes them a dangerous prospect in the knockout phase of the World Cup."No-one has thus far tackled with more passion than the Argentinians. Their work ethic and dedication are impressive," Horak told Volksblad."One gets the feeling that the Pumas are even willing to climb over each other in order to execute tackles - they are clearly playing for each other."The Pumas tackle the All Blacks in Auckland on Sunday. "Their defence will be advantageous, as teams that defend and kick the best, do well in the World Cup."He nevertheless also rates the New Zealanders' defence.The Pumas have conceded only three tries thus far in the tournament to the All Blacks' six.Horak also gave his opinion on the Springboks' defensive system, stating there is room for improvement."Nothing lacks with theirs (defence), but it looks as though the Boks are not yet completely working together as a team when it comes to defence," said Horak.