Pawlenty was the safest choice possible for McCain. He wouldn't have delivered Minnesota, but he would have put Ohio, Wisconsin, and maybe even Minnesota in play while McCain playing well in Florida and Virginia with the military vote. He would have made then-Sens. Obama and Biden to fight for Iowa's 7 electoral votes. He would have been boring and unexciting, but with McCain picking him, it would have made no news. He would have kept the spotlight on McCain, instead of Palin taking all of McCain's spotlight.
John McCain made a mistake in not choosing Tim Pawlenty because as a result of it, he lost his election. Sarah Palin was not necessarily bad, she was in fact too extreme and it backlashed against John McCains campaign. On top of that, John McCain was too extreme in his views as well and it backfired against him as well.
Tim Pawlenty is a dull, bland guy from the Midwest. Yes, he was a governor of a major Midwestern state (Minnesota), but he would not have energized the conservative base as Palin. He would be characterized as a safe, dull choice, denying the McCain campaign of what they need. He would have not won Minnesota either.