Fact is, no one knows, but it's sure as heck fun to speculate. The Hound definitely makes sense. Realistically can go through a long list of characters that you could justify as Azor Ahai:
Beric seems to obvious to me given the whole flaming sword in the promo.
Jon seems wayyyy too obvious, even though it would make perfect sense.
Bran would make sense, but he can't really do much unless he kills the Night King in one of his visions.
Jorah is more of a wildcard pick, but also makes some sense given his journey.
The Hound makes great sense, especially when you consider he is literally the opposite of his brother.
Jamie theoretically could make sense, but he is more likely Volunghar (SP)
If I had to put money on it, I am taking the field.