The good ending of number 8. All of it. The world is safe (it always was), Percy enjoys his last few months on earth before passing over peacefully to see his best friend, and Ben and Alice move in together and have Babies Ever After. It's also the only ending where Ben and Percy part ways with an handshake... that turns into an embrace.
The other good ending starts bittersweet but gets better. Ben eventually reunites with Alice, although there's no mention of Babies Ever After.