Please help! What is the most dangerous carcinogen?

No simple answer... Carcinogen is a catch-all term for anything, including things commonly thought of as safe, if applied/ingested in doses/frequencies which eventually lead (or are believed) to increased rates of cells transitioning to cancerous physiology (i.e. Grow without respect to useful function/cooperation with neighboring cells ;/or start growing in other body locations). No complete list exists, too complex.