Obama/Biden.
If McCain was running his campaign as the genuine "maverick" he was in the 1990s and 2000 Presidential campaign, then I'd seriously have a hard time choosing. But if the previous case occured, the choice of
Palin for VP would have swayed me more to Obama/Biden. Mitt Romney or
Jodi Rell* would have been better VP picks for McCain (and either could have helped sway my vote towards McCain), as they both have much more experience, and have demonstrated they can get elected to Governor in very blue states.
*If Jodi Rell, a Republican governor, can sustain an average of 75-80% job-approval rating in the blue state of Connecticut for the past four years, she must be doing something right (which is one of the main things I look for in candidates). 