Taking into accounts Hitler's lack of strategic insight (esspecialy during the later stages of the war) it is easy to opt for the obvious shock targets like London.
Hitting London would have however done nothing to get the Western Allies on his side.
Leaving hindsight and stabbing in the dark behind, the facts are as follows
Hitler had a pathalogical hatered of the Russians.
Hitler hoped in the beginning of the war that England would take his side. Note the effort made during the initial bombings of London not to hit any targets west of the East end and the docks. The blanket bombing started only after the invasion of England had been canceled, and England had made it clear that there would be no co-operation.
In late 1944 Hitler's strategy was to split the Western Allies, thus frustrating or halting their advance through to Germany. The Ardennes Offensive was meant to do this, as well as trying to re-take Antwerp to deny the Allies the desparately needed harbour for their supply.
Hitler did not want to defeat the Western Allies ( he may himself have realised that this was not going to happen), he wanted to sue for peace. After that, with or without the Western Allies, he would have thrown all his resources against Russia.
Hitlers occupation of Western Europe had little to do with ideological doctrine, it was purely to obtain those resources he needed for the Third Reich (and the war against Russia). Germany had (and still has) only a very small coast line, which is easily blockaded) Holland, for it's Harbour.
Belgium, for coal and harbour.
France, again coal and harbours, as wel as the heavy steel industries in the east. It is telling that the Germans only occupied the nothern part of France, as the south holds little resources... well, apart from Wine.
If Hitler would have had his bomb on time, he would have dropped it on Russia. The effect of that would have been enough to stop the Western Allies as well.
Cheers
Henk