I don't think it is rocket science.. The "best" photos from the perspective of those looking at them are the ones that give an accurate idea of what those in the photo looks like. That would include: current, non close-ups, both people in the couple, hopefully not a selfie bounced off a mirror in the bathroom. Also recommended is not having dirty clothes, unmade beds, and anything that makes your life look trashy in the background. Guys should try to have at least one photo where they are smiling.
The best from the perspective of those providing the pictures should be that same. Try to sneak some personality into them without being over obvious, political, bragging, etc.. A photo where you are soaked in mud and laughing? Excellent. Holding a gun and flipping off the camera? Not excellent.