"More deadly" is a weird concept. After all, "dead" is "dead"--unlike the film "The Princess Bride," there is no "mostly dead" in the real world.
So it comes down to numbers and definitions. It's hard to fault the earlier answer stressing the extreme lethality of the 2004 tsunami; it killed about twice as many people as the worst fire-related disaster I can think of off the top of my head (the fire-bombing of Tokyo in WW II.)
But there's nothing that makes one or the other inherently worse than the other--though fire will rarely be so widespread as was the casualty zone of the 2004 tsunami.