Wait a second, in another thread you suggested you were "seroius" about Palin being a good pick for Romney and that without her (or two other people you named) he would definitely lose. That's strange.....
Now, in terms of the McCain campaign...soccerboy nailed it. Palin was the better candidate for VP than Romney. The questoin is "better", not "more qualified". McCain had an issue with the base, lagging behind in terms of motivation which hurt donations and grass roots efforts. This was especially highlighted with how popular Obama was. Additionally, he was suffering from "Old White Male" syndrome with the "historic" nature of his opponents campaign. Mitt Romney was not much more popular with the base than McCain, was another "Old White Male", wasn't much mor Charismatic than McCain, and brought very little to the ticket. Palin presented him with someone that could rally his base, encouraging more turnout, donations, and grass roots efforts. She also would've allowed him to return to his moderate message to try to win over Independents while she placate the base (A strategy his campaign failed massively at). She also presented a counter to the "historic" nature of Obama's election and to the typical Republican image that was being highlighted by the Democrats at that time.
Palin was the better choice of the two for VP on that particular ticket.