I tend to use a copper grease (light application of course) as the organic compounds flash off over time the copper remains (and provides a good electrical contact!!) As the copper is soft when it comes time to get them out for inspection, it's a very easy affair. I never install a bolt (spark plug) un-lubricated. I just use normal grease on non electrical conductive or non neat affected components
Copper grease is your best choice vs other metallic based anti-seize products, as copper is less reactive than both Aluminium and cast iron. Nickel and Zinc anti-seize products 'may' undergo a galvanic reaction, (more likely on iron head engines.)
Regards
Jordan