The answer truly depends on what the original poster is needing whilst in BOS. If all the time spent there is going to be centered around business/activites in Cambridge, then stay there. One would be pleased with the Charles or the Sheraton Commander (hit and miss luck here, though).

As for BOS proper, one's options are many. XV and Le Meridien are both fabulous from most every perspective, but if you want to be steps away from Boylston and Newbury Street shopping and dining, my vote goes to either the Westin or the Fairmont Copley. As a *wood plat, I have good luck (not great, good) with upgrades at the Westin. Just understand that with precious few real suites in their total inventory, a Plat upgrade will be to a corner room or a jr suite/parlor only. Having said that, the views are to die for and the quality of accomodation is top drawer.

I need to add that I strongly feel that the Sheraton is a lesser property than the Westin if one is attempting to decide between the two, all other things being equal. While the Sheraton is fine, it is very much an older hotel with some of the constraints that come with aging properties (such as noise issues, narrow hallways, slow elevators, poor ventilation systems in some public areas that allow odors to linger, etc). The last time I stayed there as a Plat, I was given a very large suite on the top floor. Trouble was, the decor was really really bad (foil wallpaper in one bathroom, folks.) I would've been far happier in a spotlessly clean, newer standard room in the classier Westin.

Just my two cents. Other people would have been wowed by the Sheraton suite I had and would call me nuts.