Tettamanzi would be my bet too. His comments during the G-8 meetings in Rome gave him credibility with those interested in "social justice" issues. Yet he is also considered conservative on most moral and theological issues.
My guess is that this combination would be appealing to Latin American and African cardinals, who if they can't garner enough votes for someone from their region, might unite around Tettamanzi.
Popes often emerge as compromise choices. For this reason my hunch is that Ratzinger is not a likely choice, at least if the voting goes more than a couple of days. Everyone knows where he stands. If his supporters don't have enough votes to ram him through in the first couple of rounds then they will also begin looking around for an acceptable alternative.
Tettamanzi seems like a choice that would be acceptable to a variety of these voting blocs.
The new rule allowing a majority to elect a Pope after 10 days does change the calculation though. If a bloc with a majority (but not a 2/3rds) emerges they will have to decide whether or not to wait out the ten days or not. Since this is a new rule, I wonder how many cardinals would wish to depart from the tradition of election by 2/3 majority?