My experience has been they both offer pretty much the same discount. Last year we were not able to get the MKC discount for our hotel but the AAA discount was available and it was the same percentage off as the MKC now DC. I believe the same is true as far as park passes are concerned.
Lisa
CBR - 10/98
BC - 10/98
BC - 6/00
GF - 9/00
Dolphin - 6/01