AFmom, Fantasmic is soooo much better at DL! Just to see it in the middle of the park, instead of in a "theatre" setting makes it seem so much more Disney-magical. Even the storyline is different--the whole PeterPan story appeals to me much more so than the Pocahontas plot at MGM. Also the use of the "real" park boats instead of the smaller show-boat versions is nicer too.
Don't get me wrong, I still love Fantasmic at WDW--but if I had to choose one, it would be the one at DL.