As most have said, the natural ending is the best. I generally hate good endings when it feels like some Deus Ex Machina appears and everything just magically fixes itself. On the other hand, I don't care for bad endings when its predictable.

I prefer dramatic endings that catch me a bit off-guard and can be interpreted in many different ways. Cowboy Bebop, Blade Runner, and Pan's Labyrinth are wonderful examples. But ty endings that are a bit predictable are annoying, especially since this usually is a sign the film was bad overall. End of Evangelion and Requiem for a Dream are fine examples.

I don't care for fairy tale ending unless I'm watching something I know should have one like a Disney film or a comedy. I guess I have a bias against happy ending's cause it feels completely unrealistic to me. Its more believable to watch an intergalactic war between humans, aliens, demons, and demigods riding my little ponies than it is for everything to come together and have a "happily ever after" for everyone involved. I don't know why, but I usually don't accept endings that end on a completely good note.