Will your traditional contributions be fully deductible? If you're making decent sized 401K contributions, or have other above-the-line deductions then probably if that 120K is a gross-income figure. Or if you don't have access to workplace retirement plans. But any tIRA contributions that are not deductible should definitely go to Roth.
Also - if you change your mind between now and April 15th (technically October 15th 2016, but that would require filing an amended return), you can recharacterize your contributions between Roth and Traditional for 2015, so don't let perfect get in the way of good - get the money working for you ASAP!