The Marriott Courtyard is in an excellent location, just a few steps outside the wall. Mme. 13F and I stayed there just a few months after it opened (5+ years ago?). I recall the service was excellent, however we didn't use the restaurant for anything other than breakfast. It may be the best MC I've ever stayed at.
The Le Chateau Frontenac is an icon. If anyone goes to Quebec City, they want at least a view of LCF, especially if they can't afford to stay there. I've stayed at many Fairmont properties and can't imagine the service being any less that fantastic at any of them. At LCF, you will risk tripping over tourists at every turn. The hotel gives guided tours.
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13F