Marble and Granite Countertops are very similar, sometimes they are confused even by professionals, but they have important differences.
Granite is generally harder.
Both are natural stones and have the beauty and blemishes associated with natural products.
Both Marble and Granite are porous materials and need to be sealed. Sealers have become better over time and may last as long as a decade or more. Know the lifespan of the sealer put on your countertop and make sure you reseal as necessary.
Granite requires less maintenance that Marble.
Granite is generally lower in price than marble.