Ask Siri for directions and by default she will throw up an Apple Maps solution, which means you'll probably get lost. But it's actually really easy to get her to give you directions using Google's maps — and it doesn't even require a hack.
As JailbreakNation shows in this video, adding the phrase "via transit" to the end of your Siri voice command forces the software to use Google Maps instead of iOS's native cartographic car crash. So instead of saying "take me to the nearest [INSERT DESTINATION]", just say say "take me to the nearest [INSERT DESTINATION] via transit", and you're golden. Easy! [YouTube]