High level politics is about access - meaning access to power by those who support their candidate. If my friend is running for president I will vote for him since I have access to him.
This is one reason why incumbents typically win reelections. This is also why Governor George W. Bush was nominated over Senator John McCain for the 2000 Republican Party primary. Since George W. Bush is the son of a former president this gives the first Bush's former supporters access to the current presidency.
Using this reasoning, Senator Hillary Clinton stands the best chance of getting the Democratic Party nomination for the 2008 presidential election. Her election to president gives former President Bill Clinton's supporters access to President Hillary Clinton.
But, the Democrats face an obvious wildcard among its two current front runners (Senators Clinton and Obama). Despite my reasoning are Americans ready to elect either the first woman or first African-American president?