A "Factory Reset" is supposed to leave the personal stuff on the phone. Not I say 'supposed to' as things happen. A "Hard Reset" is to completely wipe a device and reinstall the original software only, all personal data gone.
Before doing either, I would really suggest backing up your personal data (contacts, music, photos, etc.) to either a cloud account or a computer so that you can put it back on the device after the chosen reset, should you need to.