well, Chiellini and Bonucci are looking very well together and Barzagli, when he returns, will need time to regain his usual form (if he regains it at all). i would try to slowly reintroduce him into the team and rotate the 3 of them depending on th opponent. maybe field a back 3 sometimes too or Chiellini at LB against smaller teams to keep them all in shape. but if we presume Barzagli regains his old form then i see Chiellini as the better partner to him than Bonucci. the 2 of them are our best CBs and should be considered starters. but its also hard to ignore Bonucci when hes playing so well so lets see what Allegri will decide after having them all fit. id trust a Chiellini Barzagli partership more in a CL QF against a top team than one of them with Bonucci
