The best place in terms of location for convenience of the client as well as lots to see and do is the Copley Square area.  There are many very nice 3 and 4 star hotels there, but of course they are all very expensive, especially this time of year on account of college graduations and people coming to visit as the nice weather arrives.  Boston has had a chronic shortage of hotel rooms that won't be alleviated, if at all, for a few years when a few new hotels come on line.

Personally I like the western suburbs, along route 128 aka I-95 and the Mass Pike, aka I-90.  They are convenient for the guys coming from the west and have free parking.  The rub is that there isn't much for you to do out there during down time.  They are a lot more affordable too.

The airport hotels tend to be the biggest bargains as they are fairly cheap and easy to get to.  If you like watching airplanes land and takeoff, then you're all set