A good rule of thumb is that once your marginal tax rate is in the 30% or higher brackets, then you should switch to the traditional type accounts to save on taxes now. I don't know any officers with a taxable income over $178,650, which is when the first marginal rate over 30% kicks in. The 28% tax bracket doesn't even kick in until $85,650.
Caveat: if Congress doesn't come to an agreement vis-a-vis the fiscal cliff and the extension of the Bush tax cuts, the rates will likely go up for everyone:
http://www.forbes.com/sites/moneybu...deral-income-tax-brackets-and-marginal-rates/
Meaning that this 30% rule would kick in at a much lower income level of $87,850 for single filers and $146,400 for married filing jointly. Much easier threshold for the more senior officers to meet. That said, those expecting to retire with a long time in service (25 years or so) should still take advantage of Roth retirement vehicles, since their pensions are determined by their salaries for the last three years of service, which will invariably be much higher than their starting salaries.
For people who joined the military after September 8, 1980, your pension (which you are eligible for if you retire after at least 20 years of service) is the average of your 36 months of highest basic pay, which is usually your last 36 months in service. If you retire at 20 years of service, you get 50% of that figure each month. At 30 years, you'd get 75%, and at 40 you'd get the full 100%. In the extreme, consider someone with 40 years of service, meaning in the up-or-out system they'll have gotten 40 years of promotions and COLA adjustments, and their pension will be the same as their salary when they retire. They'll be in a MUCH higher tax bracket when they retire than when they started, which means a Roth would've offered them significant tax savings.
TL;DR: considering the military is an up-or-out system, raises/promotions and COLA's combined with a generous pension in retirement for people who serve at least 20 years generally make the Roth TSP and Roth IRA the better choices for servicemembers.
EDIT: Disregard what I said about COLA's, it's my understanding that next year, whatever the numbers are, the tax thresholds will be linked to the CPI and adjusted each year in the same way the COLA adjusts paychecks, so it's irrelevant, but the rest still applies.