The Ren waterfront is actually not near anything but the Convention Center. There are some excellent restaurants in the area, but there is no compelling reason to stay there. It is a new property.

The Long Wharf Marriott is right in the middle of a lot of hopping activity. Walk out your door, and there is the entire waterfront development, Faneuil Hall Market etc.

Copley, either the FS Marriott or the CY, is also in the midst of plenty of activity.. shopping, restaurants and nightlife.

If experiencing a vibrant city is your mission, I would say anywhere but the Ren. jalves has it correct in reply #16 above.