What problem are you solving? What stage are you at in development? Are you looking for basic validation of your idea or getting validation for potential features/tweaks?
If you are still early on, I would start with "What do you use currently to ________?" Where the blank is the problem you're trying to solve better than it is currently being solved.
If you are still early on, I would start with "What do you use currently to ________?" Where the blank is the problem you're trying to solve better than it is currently being solved.