All th halls have good and bad points, I'm at Rankin in Carnatic, which is meant to be the worse of the halls off campus, however, I wouldn't change it for the world, without doubt I'd say facility wise Dale was the best hall on campus(Own laundry, squash courts, library, pool table, snooker table, massive TV room etc etc.
As for the halls themselves, food is pretty much the same at both, and as for busses, often there's little room left for those at Greenbank by the time the bus gets to them.
As for rooms, on the whole Greenbank rooms are nicer than Carnatic's, but it's accepted that carnatic has a better atmosphere.