What should I set as the front axis when exporting fbx from Blender to Unreal?

I want to know the export settings of fbx under blender to unreal. In some forums, it is mentioned that + x is forward, but when I tested in my pc, + is there in front, because when I align the scene in front view, + y is directed to my side. but it is suggested for the export fbx that we had to set -x as forward, why?

What should I set as the front axis when exporting fbx?