Roth IRA and income tax

I would like to double-check with you on this, though I asked some of you before.

To put it simply, I'm going to transfer $25,000 from my retirement plans (401K) to Roth IRA.

I've got two options: 20% federal tax now or withholding it until the tax-filing time next spring. 

The thing is even with the addition of $25,000 to my annual income, I'm still in the 12% federal tax brackets. 

Do you think I can get more benefits from paying the tax later (in the 12% brackets) than paying the federal tax (20%)?