Personally, I'd avoid Fagles' translations - I've found him close to neither the letter nor the spirit of the Greek in Homer, and have no reason to think his tragedy better. But some people seem to have a higher opinion of him.
Personally, if I had to choose just one version to read, it would be the versions collected in Hugh Lloyd-Jones (translator), Aeschylus: Oresteia (London : Duckworth 1982). In the US, these translations were originally published by Prentice Hall in 1970, but the current edition is from the University of California Press, and happens to be on sale from them if you're ordering within the US and use the discount code on the UC Press blog (
http://ucpress.typepad.com/ucpresslog/2009/09/bigsale.html):
http://www.ucpress.edu/books/pages/1437.php
Another well regarded translation of the whole trilogy is that of Richmond Lattimore in the Chicago series:
Richmond Lattimore (translator), Aeschylus I: Oresteia (Chcago and London : U. of Chicago Press 1953) ISBN 9780226307787