The winner depends on the political environment, and the strength of the campaigns. Walker would be the change candidate, while Clinton would represent someone who can iron out the kinks of Obama's policies.
The Veeps probably won't make a big difference. An argument that one isn't ready to lead can apply just as well to the other. Rodgers will be in her sixth term in Congress, a member of the leadership, so there's a strong claim for her on the ticket as someone who could help a Washington outsider govern. Bullock would be a first-term small-state Governor, but he would likely be a good surrogate in the west, make the Clinton campaign briefly appear more ambitious, and add a new face to a ticket led by someone who has been a national figure for 25 years.
This might just lead to an electoral tie, with Walker taking the two most conservative Obama states (Ohio and Florida), his home state of Wisconsin, and the neighboring state of Iowa.
