Magnetite is the best quality iron ore.

Magnetite, Hematite,  Limonite, and Siderite are the four major iron ores. 

1.  Magnetite (Fe₃O₄) is the richest of the common iron minerals which contain 72.4% iron. It is darker than hematite and it varies from deep dark brown to blackish in color.
2.  Hematite (Fe₂O₃) nearly contains 70% iron and is mostly reddish. Some hematite is almost black or even blue.
3. Limonite (2Fe₂O₃.3H₂O) or brown ore. It contains 60% iron content. Its colour ranges from yellow to dark.
4. Siderite (Fe₂​CO₃​), contains about 48% iron. 

Thus, magnetite is the best quality iron ore.