what you save now in a traditional is the marginal tax rate, and when you withdraw, it is taxed at the effective tax rate - that will of course have some unpredictability and will be influenced by other variables, but i assume will be less.

That's a good point, Paul. But don't forget Social Security payments (if any) are likely to be taxable chewing up much of your lowest brackets. And required minimum distributions beginning at age 70-1/2 can be a burden often taxed at the highest rates.

Roth is the best way to go for most people if they qualify. Others can do OK if they plan ahead and carefully ration funds to keep distributions in lower tax brackets. But that is harder than you think.

And note that extra taxable income (MAGI) pushes you into higher Medicare premiums that can raise your costs by several thousand per year (under current law).