It's a tough choice. Both of them have their strengths and weaknesses.

Obama is clearly the better speaker, with his powerful oratory, good delivery and charisma. But Biden is no slouch when it comes to speaking either.

Both men are smart enough to know when not to use their own voice as well. It's hard to imagine either of them making a gaffe in public that would get them into trouble.

Biden has a better understanding of foreign policy than Obama does, but he's not much better on domestic issues such as education reform or health care reform. He's more concerned with social issues like abortion rights and gay marriage than Obama is, which makes him appear less liberal overall to some voters. However, Biden's record on these issues suggests that he would govern differently than Obama has done.

Obama has a better record on economic issues like job creation and reducing unemployment than Biden did as vice president; but I think Biden's record on these issues was actually better overall.