Traditional contributions cut today's tax bill and are taxed on withdrawal. Roth contributions are taxed now and come out tax-free later.
The core question
Is your marginal rate higher now or in retirement? Higher now favours traditional; higher later favours Roth.
When Roth usually wins
Early career, low bracket years, gap years between jobs, and anyone who wants no required distributions later.
Splitting the bet
Holding both gives flexibility to choose which bucket to draw from each year, which is often worth more than getting the forecast right.
