We've stayed at the GCH and the DLH. I prefer the DLH - the rooms are noticeably larger and we have had excellent service. The pool and grounds are very impressive, too. The GCH is nice, and in a great location, but I was a little disappointed with the rooms and the service didn't seem so good (but maybe we were just unlucky). The DLH is literally a 2 minute walk from the Downtown Disney monorail station, which connects straight into Tomorrowland of Disneyland Park. There are lots of great restaurants and shops in DTD within a few minutes walk too.
If you go for concierge, you will be in the tower closest to DTD (forget the name, they recently changed it). Our room was in this tower and we had awesome views over DTD, California Adventure and towards the Disneyland Park. It was really neat.