One note of caution with the chart is that it only takes into account the candidates' current positions, rather than their past records. Obviously, for Giuliani, his rhetoric is backed up by his record of accomplishing tax cuts in the hostile environment of New York City.
But the chart also gives an equal number of check marks to Fred Thompson and Mike Huckabee, and Huckabee gets credit for signing the "no taxes" pledge, which Thompson didn't. But in reality, nobody can seriously believe that Huckabee would be better on taxes than Thompson, given that Huckabee was a net tax hiker in Arkansas, and Thompson has a stellar voting record on taxes.