I would certainly second MrBoo's recommendation of the Baltimore Waterfront Marriott as a very nice property. When I stayed there I was lucky to obtain a harbor-view room and the view was fantastic. I was living in San Francisco at the time and I remember thinking, "There is no hotel at home that has a view like this." The harbor was right across the street from the hotel, and I thoroughly enjoyed watching all the waterfront activity. This hotel is also central to anything you want to access in downtown Baltimore. It's really a big city hotel with a resort view!
I had a great experience there, and if I compare that experience to the less-than-a-year ago experience I had staying at the J. W. Marriott in San Francisco, I'd choose the Baltimore property (where I paid much less) any day. Everything that Travelpe just wrote about the J.W. seems to summarize the way I felt. As a former resident of San Francisco, I thought I was treating myself when I returned and made a reservation at the J.W. I had stayed more than once at the downtown, regular Marriott and also at the Renaissance downtown and enjoyed both very much, despite their large size. But, as Trevelpe points out, everything at the J.W. seemed a bit worn around the edges. Additionally, there was only one restaurant, and it seemed a bit pretentious to me, and also a bit pricey. I had better meals when I went out to other downtown restaurants, in fact, restaurants in other hotels, e.g., the Donatello and the St. Francis. My experience at the J.W. was ok, but only that. I remember wishing that I'd chosen to go back to the downtown Marriott or the Renaissance.