Can someone explain the difference between Fu Jai Pai, Hung Gar and Tiger style kung fu?

Fu-Jow Pai and Tiger style are the same and the original name of this kung fu system was called Hark Fu Moon (Black Tiger System).

Hung Gar is a southern Chinese kung fu style and is a system that combines the tiger and crane kung fu styles.

I'm not trying to brag, but i once visited a Hung Gar school to watch a class and the teach wanted to know if i practice any martial arts, i told him Wing Chun, so he insisted that i fight two of his students, i didn't want to, but he kept insisting, so i beat both of his top students and then left the school. It could be that the students in that school did not understand how to properly apply the principles of fighting.

If you choose between the two, i think you should go with the black tiger system.