Both--both have their pluses and minuses--mainly for the Roth there are income restrictions for contributions (we were able to convert this past year under the conversion exemption last year). Not everyone CAN contribute to a ROTH.
The main consideration is do you think you will be in a higher tax bracket NOW or LATER (when you retire). Would you rather pay tax on your investment NOW or LATER? For us, with 3 kids, rental property, home mortgage, college expenses, our effective tax rate is very small-so it makes sense to contribute to a ROTH now. If your tax rate is very high-say married couple, renting, no deductions, it probably makes more sense to contribute to a traditional IRA but there are so many other variables that go into this decision too.