Roth is only the obvious choice if your marginal rate is 0% or below - if there is nothing to be gained with a deduction this year. At any current marginal rate above 0, you could come out ahead by going traditional. Obviously, the higher your marginal rate today, the better traditional looks.
Also - due to the way certain tax credits are calculated, the marginal tax rate can be shockingly high at certain lower incomes, so even if OP determines 25% = traditional, 15% = Roth, that doesn't necessarily mean <$37,950K = Roth for a single person, < $75,900K for married filing jointly.
Example: You do a draft of your taxes in January 2018, and you find that your AGI is $18,600. Standard Deduction, 1 exemption, filing Single. You have $100, you think "I know, I'll put this into a Roth IRA for 2017!" Marginal tax rate is 10%, so Roth makes sense, right? You forgot the savers credit. If you put that $100 into a traditional IRA, you'll get a 50% credit instead of a 20% credit - so your marginal rate on that $100 is actually 40% - ($10 saved on tax + $30 additional credit) / $100.
And you've got to factor state income taxes in as well. Particularly if you're willing to retire to a state with no income tax.