Choose the Renaissance Harborplace Hotel, just a block from the harbor in Baltimore. The location is perfect, and theoretically you could walk from the hotel to Camden Yards but it's slightly far away so a cab could get you there cheap within a minute or two (depending on traffic!) If you want to shop for anything, the hotel is located above a relatively quiet mall, Harborplace, that is a couple floors high and more upscale than most malls. As for the rooms they are decorated nicely and comfortably. If it matters to you, you could spend like $30 and get a great harborview room on a higher floor. Also, I think the hotel was recently renovated so book a newly renovated room.
Here is some more info:
http://www.tripadvisor.com/ - read traveler reviews of the hotel (make sure you type in Renaissance Harborplace Hotel)
http://www.marriott.com/hotels/travel/bw… - the hotel's main website
Have a good trip!!