Is it a split flap, a fowler flap, a plain flap, a slotted flap, a slotted fowler flap? Is it a flat bottom airfoil, a semi symmetrical or full symmetrical airfoil? Is the aircraft flying at a greater AOA?

YOUR QUESTION DOESN'T HAVE A ONE-SIZE-FITS-ALL ANSWER.....If you start a post about something requesting an answer, you should try and work on your internet forum dialogue.

In general, very general- split flaps will have a higher drag/lift ratio for any setting. This is due to the separation of airflow top/bottom of the airfoil. Fowler/plain flaps will have higher lift/drag ratio at lower AOA in most settings due to the increasing camber of the airfoil.

In short- go with the manufacturer settings.