FKM remains the default fluoroelastomer for hydrocarbon, fuel and mineral-oil service. FEPM becomes relevant specifically where amines, steam or caustic chemistry attack standard FKM — it is not a general FKM replacement. FFKM sits above both in chemical inertness and temperature ceiling, at a significant cost premium, and is reserved for applications where FKM and FEPM chemistry genuinely cannot cope. The selection question is never "which is the best material" in the abstract — it is which is the most economical material that reliably handles your complete fluid, temperature and pressure profile.