As a St. Louis native (where Enterprise is HQ'd), I do prefer renting from Enterprise. Their level of customer service can't be beat, no matter if you're in STL, Chicago, San Francisco or even Calgary.
I found a "special" online for a one-day Enterprise rental last week. When I arrived at YYC, there were two very friendly gentleman at the rental counter to greet me and handle my paperwork. And in true Enterprise fashion, the car they had for me was clean and another gentleman helped me inspect prior to leaving the airport.
This was a very quick trip in and out of Calgary, so I only had the vehicle for 18 hours. No need to refill the gas tank. I was also able to drop off at 4 am at the airport the next day and leave the car keys in a drop box.
Why 4-stars instead of 5? Driving around in a compact car on icy roads is scary! I wish they'd offered an upgrade, I'd have gladly paid it for AWD on a January day in Calgary. Navigating the highway with such a small car and not a lot of traction wasn't ideal.
But having grown up driving in subpar conditions has me well trained. I survived. But a novice might not have made it out unscathed.
That's it! I would recommend Enterprise for your vehicle rental in any city.