I spent years confused about this and I want to write the explanation I wish I'd had.

Traditional IRA: you contribute pre-tax dollars (or deduct from taxable income if eligible), investments grow tax-deferred, you pay income tax when you withdraw in retirement. Best when your tax rate now is higher than it will be in retirement.

Roth IRA: you contribute post-tax dollars, investments grow completely tax-free, qualified withdrawals in retirement are tax-free. Best when your tax rate now is lower than it will be in retirement.

For most people in their 20s and 30s who are in lower tax brackets: Roth is usually the right call. For high earners in their peak years who expect a lower retirement income: traditional often wins. The uncertainty is that you don't know your future tax rates, so many people split contributions across both.

The income limits for direct Roth IRA contributions in 2024 phase out above $146k (single) and $230k (married). Above those limits, look into the backdoor Roth.