Tough call as there all classics but overall from this list have to go with Quartz 'Stand Up and Fight' just for Mick Hopkins guitar work alone although Tygers of Pan Tang's 'Spellbound' remains my favorite within the entire genre.
A few other favorites that come to mind would be Angel Witch's 'S/T' debut, Blitzkrieg's 'A Time of Changes', Cloven Hoof's 'S/T' debut, Dark Star's 'S/T debut', Demon's 'Night of the Demon', Grim Reaper's 'See You in Hell', Iron Maiden's 'S/T' debut, Paul Di'Anno & Dennis Stratton's 'The Original Iron Men 2', Praying Mantis' 'Time Tells No Lies', Raven's 'Nothing Exceeds like Excess', Satan's 'Court in the Act', and Saxon's 'Wheels of Steel'.