Cornell is less accessible than the other two in terms of traveling and getting around and out. There are some cool waterfalls nearby, and there is Ithaca Commons making up its relatively small downtown, but other than that it is off to itself.
Tufts is within Boston Metro, which is fun to travel around with the T. I like Boston as a city. Ithaca is nice as a place to stroll around for a couple days in my opinion, but it will get boring quickly.
George Washington is also in a nice part of DC with a good subway system (Washington WMATA is better organized than Boston MBTA in my opinion… but MBTA is much older, so back in the early days that may have been the best they could do).
Cornell is good to be a little isolated. Boston or DC for the city feel.