In my opinion, Obama needs someone who will continue his whole theme of "change".
Worst Pick
Hilliary Clinton: I think that while she excited some of the older poorer democratic base, she rubs conservatives and independents the wrong way. I think conservatives would love to see Obama pick her because they could more easily rally against her and her husband. They could also more easily attack Obama on relying on having someone who voted for the war, going against his whole message.
Best Pick
Missouri Sen. Claire McCaskill: She could likely pick up some of those females that voted for Hillary because she was a female. Her state could go either way and having her would likely gives him a few percentage points. She also has more moderate positions that could help pursue some of those on the right.
Likely Pick
Former House Majority Leader Dick Gephardt: Gephardt has run for the presidency and scored well among the types of voters Obama is trying to reach out to lower and middle-class workers, laborers, and minorities. Also, being that high ranking, he could possibly influence some of the democractic holdouts to support him.
McCain needs someone who could counteract any sort of benefits Obama's VP would bring as he gets to pick his a week later and will need to stop any momentum that would create in the news and otherwise.
Worst Pick
Mitt Romney: I've read that some conservatives like him and that he could raise a lot of money for McCain quickly. However, I think this would be a catastrophe for McCain. Fairly or not, I think a lot of christians are uneasy about having a mormon in such a high position. I think this could allow Obama to further get an open ear from some on the religious right. McCain already supposedly has issues with some conservatives and this would not help that.
Best Pick
Condoleezza Rice: I think this would counter atleast some of the race thing and would counter any female Obama would pick. If Obama didn't pick a female, he could lose some female votes that way. The con is supposed to be that she is linked to the Bush white house but I think this actually solidifies McCain's conservative credentials. Bush proved that someone can win having the conservative vote almost exclusively and I think McCain needs to take a page from that play book.
Likely Pick
Florida Gov. Charlie Crist: He the popular governor of the swing state Florida and if McCain can hold on there, he makes Obama need Ohio, which Kerry lost last time and Obama got blown out when taking on Clinton there. Obama then is stuck with having to flip some midwest, rocky mountain states, and southern states that is not as likely as the media's enthusiasm about Obama flipping it seems. (The best predictors seems to be historical patterns, so while he may have a bit more of the minority vote than other democrats, democrats always have the minority vote, even with Kerry, and he lost).
I think the debates will be fun. While Obama beat Clinton in the debates for the most part, I think if he steps into a townhall that McCain will take him down. Obama does best with uninterrupted speechs, while McCain would likely be able to make Obama's inexperience show.
On a bit of a different note, I think it is sad that most people will end up voting for a particular person based on some affiliation. (You know Obama will have the black vote while McCain will likely get the older vote) Then those who vote for someone cuz the VP is from the same state as them. (or shares the same gender) I think people should vote based on what their policies are. Personally, I like Obama. He is the only one likely to get some health care reform and lord knows I need it. I don't think he is gonna be the change he puts himself to be, but since when does a politician follow their word? McCain changed his mind too. (think offshore drilling) They both are backing out of the positions they held in the primaries because otherwise, they'd lose. They understand that what it really comes down to is convincing the middle 20%. (Every election you see atleast 40% democrat and 40% repulican, even during landslides) Likely, its not even gonna be that 20% but more those 8% who currently have no opinion and base their decisions on the demographics of the candidates and who has the better commercial. Either way, I don't think either will accomplish much. If either just comes through on half of what they say, we'll be ok. Take care