They should choose the ending that best fits with the film, not do one or the other for the sake of it. I personally like bad endings better, but not always. Like The Mist. That was so forced that it came off as silly instead of powerful.

I'm sure a lot of films get slapped with happy endings because of test audience reactions, though. Most people want an end to be gooey and full of ewoks, so that's what most movies will do.