"The energies of our system will decay; the glory of the sun will be dimmed, and the earth, tideless and inert, will no longer tolerate the race which has for a moment disturbed its solitude. Man will go down into the pit, and all his thoughts will perish. The uneasy consciousness, which in this obscure corner has for a brief space broken the contented silence of the universe, will be at rest. Matter will know itself no longer. 'Imperishable monuments' and 'immortal deeds,' death itself, and love stronger than death, will be as though they had never been."
Wow, it tied Step by Step, hmm, going to go with...Secret of My Heart, though I love both endings and they were both endings for my favorite episode arcs.
While the other is one of the few standout endings, Secret of My Heart is the show's best ending, so it's not really much of a contest. Plus, Kuraki Mai.