When it comes to quantifying what makes the best defender it's no longer as easy to decide on the main factors. Defensive ability itself is useful, but perhaps no longer as sought after as traits such as crossing or set piece threat.
This isn't just a fullback thing either, centre backs in a three man backline need to be ball players and carriers as well as systematically sound. It's a factor to modern day football which is still a grey area. Whereas some defenders were born to keep the ball out of the goal in anyway possible, some have special attacking characteristics that suit them to aggressive positioning and forcing the opposition back.
Thomas Tuchel likes a perfect blend, as does everyone, the defensive gold is a technically gifted player that is aware and snuffs out danger, but nobody has been able to clone Thiago Silva yet.