I always have a hard time ending my stories.
I never know whether or not to make it all end well, or to make the reader question what happens after the story ends.
Which do you prefer?

In either case, the reader needs closure unless you are planning to write a sequel. If they finish and are like, what, that was it? Where is the rest of it? it will significantly hurt the value of the story. I would say go with your instincts and your skill. If you are good at making a reader passively wonder what happens next, then that is a great way to keep the story in a readers mind and is usually preferable to a story that may not linger as much.

My endings just kind of roll out of the story. How it ends really depends on the characters and their actions. Most of mine end relativly poorly for the characters, if only because it's a series and there is more to be said of their story.

It also depends on the point your trying to get across. Are the 'heroes' really deserving to win? Are the 'villians' really deserving to loose?

Personally, I like happy endings. I just don't write them all that often. I'm not sure why.