In most cases, you would use the AGI from the amended return.  When the IRS gets this year's return, they are going to check their files to see what AGI they have on file for your SSN.  The number that you enter must match exactly what they have on their files. 

In most cases, when you file an amended return, the IRS will update their records to reflect the amended (and corrected) AGI.  So for your current year signature information to get accepted, you would need to enter the corrected AGI.

If you filed an amended return (1040-X) recently:  You should probably contact the IRS to find out exactly what they have on file.  If you recently filed your amended return, the IRS may not have updated their records with the corrected AGI.  In fact, it may be several weeks or months before this gets updated.  If you contact them directly, they can let you know exactly what they have currently listed on file for your social security number. If you need to contact the IRS, you can reach their Help Desk at 1-800-829-1040.