Defenders
RB: Dani Carvajal
This one's rather easy considering the constantly shifting dynamics of the personnel available for Barcelona. While Nelson Semedo is a highly promising talent and Sergi Roberto a great professional, neither hold a candle to the wiles of Dani Carvajal... and Spain's no. 1 right-back takes his place in a back four that he is more or less at home with.
RCB: Gerard Pique (captain)
For too long now, Gerard Pique has had to hold makeshift Barcelona defences together and last season it appeared like the strain was getting to the Catalan, but with the coming of age of Samuel Umtiti (who misses out on this team purely because of the fact that he is injured, and is out till early Feb '18 according to reports) Pique has looked like he's getting back to his brilliant best.
LCB: Raphael Varane
While most of you would foaming at your mouth for the blasphemous act leaving out Sergio Ramos from any XI he is eligible for, the fact of the matter is that this season his French partner, Raphael Varane, has been much more consistent in defence... while Ramos' greatness is undisputed, Varane has all the ingredients to be an all-time Madrid great and he appears to be peaking just at the right time for Los Blancos.
LB: Jordi Alba
Last year, there was only ever going to be one winner for this position... and that would have been Marcelo. Two things, though, have allowed Jordi Alba to oust the charismatic Brazilian from the XI - a downtick in Marcelo's form (compounded by a three-week layoff due to a muscle injury) and a sudden upturn in Jordi Alba's form (the Catalan getting back to his attacking best after the departure of Neymar freed up the left flank for him once again).