I've done both, and I'd pick MNSSHP. With the Christmas time trip there was Christmas theming every where we turned. We toured gingerbread houses, did the cookie hunt and listened to stories in EPCOT, got great seats to Candlelight Processional, watched the lights at HS, saw all the decorations at AK. The Christmas party was fun, but it was another Christmas thing. For Halloween, there was some merchandise and decorations but the party felt really special. It wasn't something we could get anywhere else or at any other time of year. The atmosphere was unique, the parade amazing and different, and costumes with trick'or'treating for adults were a delight.