Stainless-steel knives are strong, do not rust and can be used on onions and acidic foods. Unfortunately, they are difficult to sharpen and blunt readily. Carbon-steel knives are easier to sharpen and will stay sharp for a long time. However, they rust easily so they must be wiped clean and dried immediately after use. They also discolor, particularly after contact with onions and highly acidic foods.
Knives made from high-carbon stainless-steel have the advantages of both carbon-steel and stainless-steel knives and yet non of the disadvantages, but they cost more.