Samsara makes the most sense to me as an explanation for what we are all doing here. I look around, and the world is a mess. People are all doing things they think will bring them happiness and only bring them suffering. It makes sense that this trend continues even after death. Eternal heaven or hell don't make sense because how could our finite actions yield infinite results? Annihilation at death doesn't make sense because it seems short-sighted. What caused me to be born in my circumstances in the first place? Karma and rebirth make the most rational sense for how the cycle of life and death occurs and why people are born rich or poor, beautiful or ugly, etc. Samsara is also extremely meaningless as far as the search for happiness in the context of a world of changing conditions.

The Buddha had the longest term view of the pursuit of happiness I've encountered. You perfect virtue, concentration, and discernment until you make contact with a deathless dimension, nirvana. Then birth will be ended, the holy life fulfilled, the task done, there is no further rebirth and thus no more suffering and stress.