Here's The Tax Policy Center * has to say about Obama's tax policy as compared to McCain's.
Senator McCain would permanently extend the 2001 and 2003 tax cuts, increase deductions for taxpayers supporting dependents, reduce the corporate income tax rate, and allow immediate deductions for investments in certain capital equipment. Senator Obama would permanently extend certain provisions of the 2001 and 2003 tax cuts primarily affecting taxpayers with incomes under $250,000 but repeal the cuts in the top two marginal income tax rates ahead of their scheduled expiration in 2010; increase the maximum rate on capital gains; raise the top tax rate on qualified dividends from its current level (but keep it below pre-2001 levels); and enact new and expanded targeted tax breaks for workers, retirees, homeowners, savers, students, and new farmers.
The two candidates’ tax plans would have sharply different distributional effects. Senator McCain’s tax cuts would primarily benefit those with very high incomes, almost all of whom would receive large tax cuts that would, on average, raise their after-tax incomes by more than twice the average for all households. Many fewer households at the bottom of the income distribution would get tax cuts and those tax cuts would be small as a share of after-tax income. In marked contrast, Senator Obama offers much larger tax breaks to low- and middle-income taxpayers and would increase taxes on high-income taxpayers.
*an organization of "nationally recognized experts in tax, budget, and social policy who have served at the highest levels of government"