A Darth Vader sound might be something like, "Krissshhhh Hhhwoooo."
In my comic we have a lot of running so having people huff and puff as though they're out of breath reads a little different based on the character. One character, say a larger dude, may have to spend more energy so his breathing would be "huff huff wheeeze huff" vs, a lighter character might be "haff haff huff haff."
Your mileage may vary. :3