#1 Atletico Madrid

Notable players who have played for them: Sergio Aguero, Yannick Carrasco, Radamel Falcao, Toby Alderweireld, David De Gea, Mario Mandzukic and Miranda
Atletico Madrid is one of the best clubs in the world and has won the Europa League on several occasions. They have finished as runners-up in the Champions League twice.
They lost to Real Madrid on both the occasions. In the 2015/16 edition, they lost out in a penalty shootout whereas, in the 2013/14 edition, they lost 4-1.
It is evident from both the cases that better strikers would have been very helpful. In such cases, they would have been dearly missing strikers like Aguero, Falcao, and Mandzukic.
If they had a world class goalie like De Gea and top notch defenders like Alderweireld and Miranda in such situations, they might not have conceded any goals.
It is fair to say that, Atletico Madrid could have won at least one of the two Champions League finals that they played in.