UEFA's four top-ranked teams -- Barcelona, Real Madrid, Bayern Munich and Chelsea -- are on a Champions League collision course after being kept apart in the quarter-final draw.

While Barcelona face an all-Spanish tie against La Liga title rivals Atletico Madrid, Real Madrid will attempt to avenge their 4-3 aggregate loss to Borussia Dortmund in last season's semi-finals.

Holders Bayern, 2-1 victors against Dortmund in last year's final, will play stuttering Manchester United, with Chelsea's tie against dark horses Paris Saint-Germain completing the last eight line-up.

Here, AFP Sports looks at the tactical factors that will help to decide which teams make it through to the semi-finals:

Barcelona (ESP) v Atletico Madrid (ESP)

- Barcelona remain the masters of 'tiki-taka', but they have lost their crown as the competition's ball retention kings to Bayern Munich, who have averaged 65 percent of possession to the Catalans' 62 percent. Last year's arrival of jet-heeled Brazil star Neymar has encouraged coach Tata Martino to adopt more of a counter-attacking style, but Barca's game is nonetheless still based on patient ball circulation, orchestrated by peerless Spain midfielders Xavi and Andres Iniesta. Under former player Diego Simeone, Atletico have adopted a high-intensity pressing game that has made them the most defensively robust side in La Liga. Los Colchoneros also pose a major threat from set pieces (a Barcelona weakness), having scored more goals from dead-ball situations (eight) than any other team left in the tournament.

Manchester United (ENG) v Bayern Munich (GER)

- United manager David Moyes was accused of regressing the club to a tactical Dark Age after they lumped 81 crosses into the box during a 2-2 draw with the Premier League's bottom club Fulham last month. They looked more like the United of old in the second leg of their last 16 tie against Olympiakos, but Robin van Persie, who scored all of his side's three goals in that game, will miss both legs of the Bayern tie with a sprained knee. Since arriving at Bayern, Pep Guardiola has instituted an uncompromising passing game reminiscent of the style he patented at Barcelona. The Bavarians passed Arsenal to death in the last 16, enjoying a staggering 73 percent of possession during their 2-0 first-leg victory. Having utilised a 4-1-4-1 system that saw full-back Philipp Lahm redeployed as a holding midfielder, Bayern have reverted to a 4-2-3-1 shape since Bastian Schweinsteiger returned from an ankle injury in February.

Real Madrid (ESP) v Borussia Dortmund (GER)

- The redoubtable pace of Cristiano Ronaldo and record-breaking signing Gareth Bale means that Real Madrid remain a formidable counter-attacking side, but coach Carlo Ancelotti's decision to switch to a 4-3-3 formation has given them better control of the ball in the middle of the pitch. Madrid are also the competition's top scorers with 29 goals -- an impressive 25 of which have come from open play. Dortmund have gone off the boil domestically since last season, bedevilled by injuries and left for dead in the Bundesliga by Bayern, but Jurgen Klopp's team remain one of the most hard-working in Europe. They have made more tackles (24.6) and interceptions (19) per game than any other side still in the competition, according to the Who Scored website, and conceded fewer shots on goal (nine per game) than anyone apart from Barcelona and Bayern.

Paris Saint-Germain (FRA) v Chelsea (ENG)

- Since succeeding Carlo Ancelotti as PSG coach, Laurent Blanc has added a dash of flair to the French giants' domestic dominance, devising a 4-3-3 system in which Zlatan Ibrahimovic leads the line and record signing Edinson Cavani patrols the right flank. In midfield, Thiago Motta, Marco Verratti and Blaise Matuidi respectively supply poise, artistry and lung-bursting energy, while Brazil captain Thiago Silva imperiously marshals the defence. After returning to Chelsea from Real Madrid, manager Jose Mourinho was quick to fall back upon the counter-attacking style with which he has forged his reputation. No Chelsea player has scored more than three goals in the competition, but in Eden Hazard, Willian, Oscar and Andre Schurrle, Mourinho possesses some of the swiftest attacking midfielders on the continent.