I will reserve any judgement about the A380-800 until I see one for real
I do know that the A340-600 is one stunning-looking plane, based on seeing F-WWCC flying out of SFO twice.
But historically, the 747 has already established its historical niche because it was the plane that brought down the cost international air travel to reasonable levels. Have you ever seen the cost of a transatlantic ticket during the 707/DC-8 days? US$500 one-way during the 1960's was considered a cheap ticket!! Today, if you find the right sale you can fly JFK-LHR for US$200 one way.