Theres a few important qualities we need in a CB this summer.
1) Skill with the ball at their feet, able to play out from the back
2) a lot of pace for playing high lines/recovering from attacking phase
3) Able to play left sided effectively
4) Long term option to keep stability at the back with Kompany
Whoever fits this bill closest, be it Mangala or Benatia, should be our priority.
I'd be surprised if we've suddenly decided Mangala is not worth it considering we knew his price in January and we willing to pay it, plus if current reports are to be believed his price will be much lower than expected.