So with 26 biweekly pay periods it sounds like your annual deductions are 192.66 Dental + 2,364.96 Health + 52 United Way Donation* + 1,252.16 403(b) = 3,861.78. Subtract that from $60k income and you're at $56,138.22. Subtract $12,200 standard deduction and you're at $43,938.22 of taxable income which is $4,463.22 into the 22%
federal tax bracket. Given that I would be inclined to say you should contribute at least that much to a traditional IRA or your 403(b) unless you expect to spend quite a lot in retirement.
Beyond that, paying 12% to contribute to Roth is probably kind of tossup. If you stay single and withdraw between $21,900 - 51,675 from tax deferred accounts in retirement then it doesn't matter, below that would favor traditional, above would favor Roth. If you get married that range would be $43,800 - 103,350.
This ignores state taxes, so if you expect to move to a lower/no income tax state when you retire that would favor tax deferred contributions. If you expect to move to a higher income tax state then that would favor Roth now.
If tax rates go higher than they are now, that would favor contributing to Roth. After 2025 tax rates will reset to the 2017 rates, which were slightly higher, under current law, so if nothing changes that would (slightly) favor Roth, and if things change towards higher taxes, that would also favor Roth. If things change to lower taxes that would favor traditional.
So, basically, if you expect to stay single, move to a high income tax state, spend a lot in retirement, and think that tax rates will go up in the future (or some combination thereof) then contribute to Roth after you've contributed about $4500 to traditional to get below the 22% bracket. If you expect to get married, move to a low/no income tax state, spend little in retirement, and think tax rates won't change too much (or some combination thereof) then contribute as much as you can to traditional.
Personally, if I were you I would be pretty confident that I would stay in the 12% bracket in retirement (maybe 10% if I got married, but that's only a 2% savings), and that tax brackets wouldn't change too much at that income level (but maybe back up to the pre-2018 15%), so I would base the decision mostly on my expectation for state taxes. If I planned to stay put I would contribute to Roth, if I planned to move to a no income tax state I would probably favor traditional.
* I don't know how the United Way donation works. It's unlikely that you itemize (unless you have a large mortgage or lots of other donations), so you wouldn't normally be able to deduct charitable donations, but it's possible there's some kind of program through your employer that makes this non-taxable regardless. At only $52 it's not likely to make a big difference to what I've written above, just don't cut things too close without confirming whether it's taxable.
