This is where the rubber meets the road. A few folks I know have asked my for advice recently and they prefer Roth, but their situation dictates traditional because they are teetering on the tax rate border. What people need to do is understand that they should contribute just enough to traditional to stay in their current tax bracket, not got all Roth 401k because it'll be tax free upon withdrawal. The gubment is going to get your taxes, today or tomorrow and for those of us with ascending careers and many years left of earning, it usually is beneficial to use the traditional and pay the taxes later. If you are loaded now or are going to receive a substantial windfall via family down the road, then Roth makes sense. Makes sense if you are under 30 and so far away from retirement that you have no idea what tax bracket you might be in.
I'm fighting off a tax bracket change myself, but know that I'll be in this tax bracket or lower when I retire. So I put it all in traditional, although I still fund my Roth IRA (have been since it was created).