tax implications on the conversion of traditional IRA to Roth IRA

Okay, this is my question.

I've got an employer-sponsored retirement plan and Roth IRA.

Now, I want to roll over the whole fund (about $1,7000) of one plan to Roth IRA.

I've got two options: 20% Federal tax pay now, or pay later during the tax filing season next year.

Which is better for me? If I pay the tax later, does this taxable fund count as income in my adjusted gross income? Even this taxable fund is added to my income, I belong to the 12% tax bracket zone. 

What do you think is the best solution for me?