I don;t think it takes much of watching Ivanovic vs Alex in training to know who is the better CB - if he gets some continuity playing and stays injury free, there aren't many SB out there as tough and tactically sound as Alex is.
I'd say the only reason why these rumours of Chelski not wanting Alex is sending waves of turmoil thru this peaceful place is that Alex had a tough season last year, injury-wise and looked shaky even when he could play, mostly due to lack of fitness and continuity, though.
Considering he's been healthy since last season, I;d imagine AVB has made up his mind as to who Alex really is and what he can offer to Chelski's defense ... and the guy has 2 years left on his contract; he seems to be looking for an extension hence all the baiting and flirting that seems to be going on lately.
All in all, I expect Alex to be their starting CB along Terry and Chelsea to be unwilling to let him go, which is the only way he could end up at Juve - Chelski to be wiling to get rid of him - considering he still has a contract with them, which they probably don't see a reason to renew just yet.