Atmosphere and student body. If you're not in a frat at UW, it's hard to make friends. Don't get me wrong, I loved my time there, but I've found it to be quite the opposite here at GU. Everyone is family here as far as partying goes.
As far as academics go, I'm at GU for law school, so I can't compare what it's like as an undergrad.
And Zag basketball > Husky basketball.