Experience has little to do with it
However...if monergism is true AND there is an eternal hell, then...as I always say, God is a moral monster (because he could save everyone and doesn't). My reason for believing in synergism has little to do with experience; it is all about the character of God.
It's all comes down to experience
However, I do not think there is any rational proof of God's goodness. I agree with Pascal, Kierkegaard and Coleridge (not exactly intellectual slouches) who all said (in their own ways) that the only proof of Christianity is in the experience of it.