I can see doing a deferred ductable ira or traditional 401k towards the tail end of ones earnings history when income is the highest. Early on though i think not doing it and going all roth would be a better choice.
Those low average tax rates in ones ramping up years would leave a traditional ira or 401k behind.
The higher years earnings would pay off since you can deduct them at fairly high rates hopefully , and take them out tax free using up your standard deductions and exemptions.
but you have to be careful doing that ,depending on when you take ss and the amounts involved. it may still be better to have the roths tax free since if need be you can apply those exemptions and deductions against your ss income possibly preventing taxes on that.
taking ss early or not and the amount you get is going to be the wild card as far as which is a better choice.
had roths existed during my early career they would have payed off far better now than my deferred accounts will tax wise.
not only because of getting my ss taxed but the rmd's are a factor too. in fact the roths still have the edge since as of now all gains after 70-1/2 are tax free.
remember ,at 70-1/2 i have to start drawing money out and if i don't spend it i have to reinvest it in my taxable accounts.
all future gains and earnings are now taxed as well as the money i had to take out.
the roths still grow all tax free on future earnings after 70-1/2.
all in all it can be very difficult to come out a head with deferred accounts once zero rmd's and zero future taxes in a roth are considered as a factor down the road.
in fact i bet in most cases the average long term tax rates one saw over a 30 or 40 year career still leave you in a lower bracket than the cxurrent one you retire at.
there is talk of taxing gains after 70-1/2 in a roth too but so far it is still all systems go for the roths in that respect.
according to t.rowe's study:
Most investors remain in the same tax bracket during retirement. However, if an investor’s tax bracket happens to drop by at least 9% and they are over 50 years old, the Traditional IRA becomes more valuable.
A 65-year old would only need a 6% drop in their tax bracket for a Traditional IRA contribution to be more advantageous than the Roth IRA in retirement.
https://www2.troweprice.com/rms/rps/...4_Roth_IRA.pdf