This absolutely depends on your current tax rate, and your future tax rate. Since you've omitted this info, I'm suspecting you don't fully understand it. The Wiki has some info on this.

If this year, you had a big drop in income, or a big increase in deductions/credits and owed particularly low taxes? Sounds good. Or if you can predict your income will increase enough to go up a few brackets in the future, converting to Roth now might make sense.

One example last week was a guy/gal going to med school after working for several years. He's effectively going to drop his income to $0 for 3-4 years, convert an old Traditional 401k to Roth, pay the income tax on that conversion at a rate of something like 10%, then graduate and eventually walk into an effective tax rate of 25%.

That is a perfect example of when to convert. Med student (hopefully) will pay more in taxes as a total percentage of income upon graduation.

If your income looks flat, or is declining (reducing hours to raise young kids? Easing into retirement? Taking a less-stressful job?) It probably doesn't make sense to convert now.

Also, if you're planning on retiring "small", meaning you'll be downgrading your expenses (moving in with kids? paid off house?) and you'll need less income in retirement than in the future, your effective tax rate in retirement could be lower than it is today if you're in the prime of your career and spending lots on kids or hobbies. Thats when it absolutely makes sense to pay income taxes in the future, and not today. Which means Traditional is the right choice.

And the third option is if you believe the USA will stop having progressive income tax and will do some flat/"fair" tax code overhaul in a 2016 Rubio presidency. In which case, I suggest buying stock in tin-foil hats.