Your iPhone's lady robot butler doesn't think that much of the iPhone. When asked "what the best smartphone is ever" she opts for a direct competitor. If its not an iPhone then what it is?
Turns out, Siri's got her eye on the Nokia Lumia 900 4G. Don't believe? Ask her yourself. The Lumia 900 is terrifically nice, yes. But the only reason Siri loves it, as TNW points out, is because Wolfram Alpha loves it.
Wolfram Alpha, the computational knowledge search engine takes facts and basic equations into consideration to provide answers to many of your Siri queries, including the one about the best smartphone ever. It pulls its information from user reviews around the world, and if you have the time to do that, you'll find that the Lumia would come out on top.