I think the back four presents the toughest decisions.
Cafu won two World Cups and was runner-up in another. But he only won the Champions League once.
Roberto Carlos won three Champions League trophies. But he only won the World Cup once. And if you care about actual balance it would be hard to pair him with a best XI left wing.
Thuram won a World Cup, and European Championship, a World Cup runners up medal and a bunch of (revoked) Scudettos. But he was equally a CB and a RB. And he only has one Champions League runners up honor. Thuram is my favorite defender of all-time, so I'm biased.
Ramos is also split between RB and CB. He only has one Champions League trophy. But he has a World Cup and two European Championships.
Maldini is split between the pre-modern era (which was probably his prime) and the modern era. He also split between CB and LB. He doesn't have the World Cup. But he's probably the best pure defensive left back of all time and has five Champions League trophies.
Puyols has three Champions League trophies, a World Cup, and European Championship. He has more La Liga titles than I care to count.
But Cannavaro won the Ballon D'Or. He was player of the tournament in World Cup 06. No Champions League titles, though.