Osmium is the heaviest metal with a density of 22.61 gm/cc. However Iridium element is not far behind with density of 22.56 gm/cc. Even it's consider that Iridium is heviest at room temperature and standard atmospheric pressure with a density of 22.65 gm/cc. These are real dense elements. You can guess it's density by weight. Almost one liter of Osmium & Iridium contains 22.61 Kg and 22.56 Kg weight. So it's not easy to lift a small block of osmium and iridium due to it's high density. 1 Imperial gallon of Osmium weight is more than 102 Kg.
The highest elements which i dealt is Mercury. It density is about 13.56 gm/cc. I still remember when I tried to pick the 5 liter container of mercury. I failed to pick than I realized the weight of can was 66 Kg.
The heaviest/densest metal is one called osmium.
@valth already wrote that the heaviest/densest metal is the osmium, but let's see the science of music:
The top 30 heavy metal bands nowadays are the Iron Maiden, Black Sabbath, Judas Priest, Metallica, Mötörhead, Slayer, Pantera, Megadeth, Anthrax, Tool, Slipknot, Korn, Disturbed, Rammstein, Lamb of God, Avenged Sevenfold, Linkin Park, Kiss, Death, Napalm Death, System Of A Down, Five Finger Death Punch, Dream Theater, Cannubal Corpse, At The Gates, Sepultura, Superjoin, Carcass, Testament, Celtic Frost, Opeth.
The heaviest is a question of taste, of course.