In a long interview with 92 Y, George R.R. Martin revealed that a reader had asked him that exact question about Daenerys’ dragon, Drogon, versus Smaug. And, refreshingly, Martin conceded that Smaug would win…
Basically, no. Drogon is a very young dragon and still barely large enough to get Dany into the sky… Smaug is gigantic, not to mention that Smaug talks and would probably have an intellectual advantage. But Balerion could give Smaug some trouble; they’re more equivalent in the size and ferocity department.
Score one for logic.
Martin also outlined how readers of epic fantasy now expect a fully realised secondary world.
Of course, fantasy goes back to ancient times: the Illiad, the Odyssey, the Ballad [sic, i think he meant Epic] of Gilgamesh. But Tolkien really invented modern, epic fantasy in its current form. And one of the things he did that was extraordinary was to create Middle-earth in such detail… Tolkien gave us all these histories, all these appendices and genealogies. And everything was rooted: it seemed as real as England or France or Germany when you read these things.