The world could possibly end in two ways. The author, if he had to perish twice would like to try both.
Fire is desire and I think ice is equated to hate. I don't think he necessarily thinks one has a greater destructive power than the other, but that his first choice would be fire/desire. This is because I think that the fire represents love. Both fire/desire and ice/hate can be extremes of emotions and the elements. Do you find it interesting that his last name is Frost?
I think the poem is about both, and human relationships like fire and ice have the power to and can be equally effective at destroying.
It s hard to pick just one line as the most important, but I guess it would have to be "from what I've tasted of desire". I think that this line speaks of the love he has had and the love of mankind and humanity. I think desire can be both good and bad. The poet uses the term in a way to say that desire has ended it all and gone so far so that there is no longer anymore, maybe it has all burnt to leave nothing but ashes? .My final thoughts on the poem are the following; this is a poem that speaks of both relationships and ending the world. The poem relates many opposites, fire and ice, desire and hate, an all consuming buring passion and a bitter cold hate. When one has experienced the "fire" only ash is left, all is gone, but if one where to experience the "ice" it would destroy but not end it all. With the ice everything in frozen and destroyed but not truly gone.