Hmm . . . if neither was trying to kill the other, I'd say Torch wins, if only because Iceman can take more damage without dying, meaning Torch wouldn't have to hold back as much. He could basically melt most of Iceman's body and heat the surrounding air until all the moisture rises away, leaving Bobby without any water to reconstruct himself from. Whereas, Bobby's non-lethal attacks would all involve encasing Johnny in ice or throwing Ice at him, and his fire would melt it away no problem before it touched him.
Now, if both were trying their best to kill each other, it would come down to who got the drop on the other, since each could kill the other one instantaneously. Bobby could instantaneously freeze every molecule of water in Johnny's body (he did it to Legion in "Legion Quest"). But on the other hand, one full-force blast of Johnny's flame would vaporize Bobby completely. So I think it's about 50-50.
Of course, this is all based on the assumption that when Torch's flame hits Iceman's ice, Torch's flame wins, but I'm fairly sure that's true.