I think Cleveland easily has the best collection of Marriott properties, especially downtown where you have four (about to be five) to choose from and really cannot go wrong.
Key continues to take top honors for me just because of the proximity for what I come in town to do, but all of them are fabulous. Staff is always friendly and while I like the Renaissances Concierge lounge better (aesthetically as well as offerings) Key is also very good.