The principal difference in policy between Clinton and Obama involves health care. Their approaches are different.
Estimates by Johnathan Gruber of M. I. T., a leading health care economist, finds that a plan resembling that of Obama would cover 23 million of those currently uninsured, at a cost of approx. $102 billion per year to the taxpayer. A plan covering practically everyone, of the type proposed by Clinton, would cost the taxpayer approx. $124 billion per year. Looked at overall, the Obama-type plan would cost $4400 per newly insured person, the Clinton plan only $2700.
Clinton's plan achieves almost universal coverage; the other, Obama's, costing 80% as much, covers only half of those currently uninsured.
Obama has demonized the idea of mandates (a recent scare mailer sent to voters resembles those sent out by the insurance lobby in 1993).
If Obama happened to reach the White House, it will become clear that universal coverage cannot be achieved without mandates.
There is a chance that if Clinton gets the nomination, she might be able to carry through and win universal health care for us. But with Obama, there is no chance.

The above is explained in a column in the New York Times, Feb. 4. 2008, by Paul Krugman.

Obama calls for the removal of U. S. troops within 16 months if the Democrats win. When pushed yesterday, he had to admit that timing would depend upon the situation- as Clinton has stated. Sixteen months sounds good, but is impossible.

Obama is a man with no clear idea of the results if his proposals were ever carried through.

Of course, no program will pass a divided Congress without compromise. Clinton is a much better compromiser and horse trader than Obama, who tends to get angry whenever someone questions him.
Hillary Clinton is the best choice for a Democrat-led change.