A Roth uses already taxed money going in, with no taxes and no withdrawal requirements on the other end. A traditional 401k uses pre-tax money going in and has specific withdrawal requirements after age 70 1/2 with all the money being taxed as ordinary income.So, if you are in a high tax bracket you will have considerable current savings by deferring the tax on the contributions, and in typical circumstances you will be in a lower bracket when you are retired and withdrawing.The Roth can be a better deal if you are young (so there is a long tax-free growth) and in a low bracket when contributing where the deduction you would get from the traditional plan would not be so much.There are other things to consider too - you may get an employer match on some 401k contributions which is like free money. Or, if you want to leave some money to heirs, the Roth with no withdrawal requirements would be a good thing to leave unless you need it late in your retirement years.