Leningrad, unlike Stalingrad, was one of the original targets for Germany. Plans for the capture of this city were drawn up before Barbarossa.

Leningrad was Russia's second largest city, main port, and a cultural capital. It housed Russia's second largest population and surpassed Stalingrad in industrial might. The fall of Leningrad would have been far more devestating on the Russian morale then Stalingrad.

Not to mention that Germany had a much larger garrison and investment in Leningrad. Capturing this vital city would have freed up hundreds of thousands of men and equipment which were simply stuck there for 3 years and a drain on Germany.

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The war against Russia will be such that it cannot be conducted in a knightly fashion. This struggle is one of ideologies and racial differences and will have to be conducted with unprecedented, unmerciful and unrelenting harshness. -Adolf Hitler