Gents-
With Smalling, Jones, Evans, Rojo and McNair, I think we have good enough CBs to challenge for the title.
Even though, the defending has looked/been haphazard at times this season, I believe this is primarily down to a lack of protection from midfield (we looked much more composed when Carrick returned from injury, and even went on a decent run), and the fact that we've been playing a 3-5-2 which exposes our weaknesses and hides our strengths. I think we've got the 2nd or 3rd best defensive record (a lot of this down to DdG).
I think Smalling this season, injuries and the red card v City aside, has really stepped up and played with a lot of composure and intelligence. He should be our number 1 CB (when fit).
Evans is playing with 0 confidence at the minute, but we all know he's a good defender as evidenced by his form under Fergie. I think he's a good option to have, but shouldn't necessarily start every game at the minute.
Jones-well, I suppose we're all waiting for the penny to drop with him. Injuries have hampered his progression, but if he has a good spell not injured, I think he can make a similar step up to what Smalling has made.
Rojo for me should be starting most matches. He can be a little rash, but I suppose we can put that down to the South American tenacity in him. I don't think he should play LB.
McNair-has a big future ahead of him.
If we take Chelsea's defence to be the benchmark, Ivanovic/Terry/Cahill/Azpili have started pretty much every game together, and it's that consistency and experience that we lack. Injuries have taken their toll on us.