It's good to think about tax brackets, but when I look at your situation, I don't really seen any either/or decisions that hinge on tax brackets.
If you can, you should max both accounts, period. Where tax-bracket decisions come in to play is if you have two alternates, and each has a bearing on your marginal tax rate. For example, if you have a choice between a deductible traditional pre-tax 401(k) and a Roth 401(k). If you're straddling the line of the 25% and 15% tax brackets, then that's a classic case of where tax bracket analysis can help. For someone in that scenario, supposing you are inclined to make Roth contributions, you might want still want to contribute enough to the traditional 401(k) until you get to the top of the 15% bracket, and then go Roth 401(k) for the balance.
In your situation, you will probably wind up squarely in the 25% bracket. And the difference between the 28% and 25% bracket is not that meaningful anyway since they are so close to each other.
Starting with your $115K salary, once you reduce that by the standard deduction ($6,300) and personal exemption ($4,000) and we'll estimate $2,000 for health insurance premiums you pay, then you're starting out at around $102,700 adjusted gross income. You're still in the 28% tax bracket, and need to lower your taxable income down to $90,750 (for tax year 2015) to get into the 25% bracket. So, I would just contribute as much as you can to deductible 401(k) and 457(b).....which is what you should do anyway.
If you can max them both, then great. If you can't max both, then the question is which one do you prioritize?
If you have a governmental 457(b) then there are a lot of advantages to that. If it's a private sector 457(b), there are some risks and negatives to this that you should read more about.
The only other thing to throw into the mix is an IRA. You make too much to be able to deduct contributions to a traditional IRA, so no point in making traditional IRA contributions when you can't deduct them. You are under the income limit to make Roth IRA contributions. If you can max all three, then go for it. But if you can't max all three, it's debatable whether you should contribute to a Roth IRA, when you're in the 25% tax bracket, if you can still make deductible contributions to a 401(k) and 457(b). I would choose the deduction over the Roth IRA.
But if you're a good mustachian, you'll scrimp and save enough to max all three :-)
Oh, and if you have an HSA, you'll max that too, right?