Settle it on the field. A playoff is the only fair means of answering the question. Who is the best team for the year in question? What would have happened if Oklahoma State would have been awarded the opportunity to play for all the marbles? Why did Alabama get another shot at LSU? Shouldn't another team have been given the chance to knock of the #1 ranked team in the country?
I personally prefer the BCS model over a play-off.
Having said this, I would scrap the BCS. I would slightly adjust the system of 30 years ago. Complete the bowls on New Year's day and two weeks after the bowls, match the top two teams as ranked by the AP.
I want to have my cake (whatever that really means) and eat it too. Keep the bowls relevant and increase the likelihood of crowning a true national champion.