I've been to both WDW and DL, and while I'm glad I went, so I can say "been there, done that," I don't ever need to go back to DL. To me it was just a very condensed version of MK, we did the whole thing in less than a day. I like the whole 4-park experience of WDW, the resorts, the transporation, etc. Just my opinion.
If you've been to DL, what one attraction do you wish they had in WDW?