Chael has improved much more, he rocked Silva, and took him down at will, people will bring up the 16:1 ratio and the broken rib but on an even playing field Sonnen is still a bad match up for Anderson, especially if Vinny has his sub defense up to par.
Sonnen is ruthless, aggressive. he's got a great chin, fantastic cardio and will get in Anderson's face trying to take him down. Vitor, Leites, Okami, Cote, Maia these guys don't have the qualities that Chael has.
Anderson can do some special things but can Anderson stop the takedown? He stopped a few in the first fight but he always managed to end up on his back and if that submission defense is what I hope it is. I think Chael seals the deal with a little more caution.
Chael via conservative decision.