I've been going to Manuel Latruwe for many years now. It has my favorite croissants in Calgary, as well as excellent desserts and coffee.
The service is good, and the location is nice especially because they have parking but are fairly downtown. On the downside, they are not cheap, they run out of things quickly, and rarely open during any busy season in calgary. Don't try to go there during the holidays or stampede for that matter, they are closed.