If I understand what you're asking, it differs like this:
CD is more restrictive. You have to commit your money for a period of time. 6mths,1 year, 3 years, 5 years etc. Savings accounts have freer access to the money, but the rate could change on you so that you're earning less money than a CD would.
The tax rate should be identical, they are both unearned income, taxed at your marginal tax rate. Hope this helps...I think I'm right, but if I'm not, you'll know soon enough on this board.