Personally I'm a fan of
Park 2 Go, I used them last summer for a week and for the price of a cab ride (about $50/week) it's well worth it.
Book in advance, drop off your car/keys, hop onto a shuttle bus that leaves every 5 minutes (they don't wait till their full, they just go) to the airport. They give you a tag with a pin number on it, you text/call in the pin when you land back in Calgary, hop onto the shuttle again, pay on the shuttle via credit card, arrive back at the lot to find your car running with your receipt on the dash.
Like I said, for the price of cab ride I find the service is well worth it, I've only used them once but the online reviews suggest that's the regular experience.