Regarding transportation.....there are GUTS buses that run very frequently to/from campus to Dupont, Rosslyn, and deeper into Arlington. There is also a Circulator bus that runs from Rosslyn through M-street (in Georgetown) to Dupont Circle.
Dupont Circle is going to be the most expensive location but it will also be where most of your classmates will be going out to bars and clubs. As someone that lived in Rosslyn last year, the Circulator was my move and I took it all the time to my friends' spots in Dupont. Living in Georgetown isnt a bad option either, as its most accessible to campus and you will go out at night in Georgetown often as well. Foggy Bottom and Adams Morgan would probably be just below those neighborhoods in terms of most desirable in my opinion.
I actually find all of DC to be very accessible and this is coming from a native New Yorker. You can walk/cab/bus/subway it anywhere within a reasonable amount of time