For my flash fiction in particular, I like to end either with a "punch" so the story has impact or with a twist, which, as is the way of these things, sometimes you'd guess at, other times you wouldn't.
I never mind being able to guess an ending incidentally because it is nice finding out whether you're right or not! I adore guessing wrong or not seeing the twist - all kudos to the writer for achieving that - as it is nice to be surprised, look back at the story and realise the clues had been there and I'd have seen them if I'd been a bit more "on the ball" when reading the tale. It is a real challenge to write those kind of surprises - though that's no reason not to try it!
I like my stories to end appropriately. This isn't the same as happy. One of my stories in my book, From Light to Dark and Back Again, ends sadly and was always meant to (but I hope makes for a good character study).
So how do your stories end?