Tough one.
Smalling - for me by far our best pure defender - Great recovery pace, strong in the air, reasonable tackler & man-marker. I worry about his handbags with VAR's inception but hope he'd be smart enough to cut that out. He has to be in there, unless we upgrade to a Maguire type aerially-dominant CB.
Lindelof - our best ball-playing CB - Composed, looks for the positive pass into good areas, decent in the tackle but a bit passive for my liking. He's weak in the air and doesn't have great recovery pace, always looked like more of a DM than a CB to me.
Tuanzebe - Highest potential - Seems a really well rounded young CB, defensively solid while also comfortable on the ball. I can see that aerially he's not exactly dominant but I'd place him above Lindelof in this department, and he seems to be improving all the time.
Bailly - Athletic / Insane - Great athleticism, strong in the tackle and certainly someone strikers will worry about having on their shoulder. Embarrassingly bad in the air and constantly injured. It's a shame as you can see he's got potential, I think he started his professional career too late to make it.
Rojo / Jones - Permacrocks. A stable CB partnership is more important in many ways than its constituent parts. These guys will never string enough games together to allow us that. I do think Jones would have been fantastic with a working body, so that's a shame. Rojo, I've never seen it, awful player.
Smalling / Tuanzebe for me, assuming no incoming CB. Gives a nice immediate balance, while allowing our best defensive talent to develop alongside a reasonably stable partner.
Lindelof / Jones / 'A. Youngster' as backup. Bailly sold to the highest bidder. Rojo sent to the clappers yard.
Edit: Maybe TFM can stick around as 5th CB? Nice to have his versatility I suppose.