You chose well. The HC Faneuil Hall is one of the worst Hyatt properties I have visited. The HR downtown is a big conference hotel and a little dated but probably the best option in Boston. Also, unless you are planning a lot of activities outside of the city, you probably won't need your car much. Boston is small/dense with most sites easily accessed by public transportation or walking, and the Regency is next to multiple subway lines. You may find that the hassle of driving in the city and parking at your destination is worse than riding the T a few stops.
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