It is faster for U.S. Citizen parents from the Philippines to petition adult single children than it is for green card holder parents?

FALSE!

It takes longer for single adult (over 21) children of American citizens to obtain green cards than the single adult children of green card holders, for people born in the Philippines. Therefore, if you are a green card parent and have a single adult child under petition, it would be best to check the current priority dates in these categories, and file the petition for your single child while you are still an immigrant vs. waiting until you naturalize.


source: http://www.gurfinkel.com/imm_updates53.htm