Smalling-Lindelof -- best balance and most stable, compliment one another (similar to Smalling-Blind).
Smalling-Jones -- if just pure defending, the best one we've got atm, at least for EPL. If opposing heavy mark our other players and let 'em two hog the ball all day long, you'll see how so bad and comedic and depressing it is.
RoJones -- the best injured duo.
Bailly-Jones -- 2nd best injured duo.
Bailly-Rojo -- used to be our best. At their best, we dominate and bully opposing attackers, both of them are also good at their feet, compliment one another. Still? unlikely.
Bailly-Lindelof -- idk, only few games just this season played together, and most of that time Eric is in low form. One impressive game iirc vs Arsenal? In theory, their different styles should compliment one another to the fullest, except aerially may be exposed. Future CB pairing? who knows. Bailly seriously need to keep himself fit and take care of his body first for that.
Smalling-Rojo -- rubbish, messy combination.
Bailly-Smalling -- same messy.