Best knife?
An old one you find at a yard sale.
Better yet if it has some rust spots.
A GOOD knife WILL rust if not cared for.
More rust means (for the most part, before you guys get excited) better steel. Less rust means more stainless, which means less edge retention.
Any blade with a high carbon content will take and hold a decent edge.
My favorite in the kitchen is a French knife or a cleaver. You can do almost anything in the kitchen with one of each.