We just returned from our first trip to DL, having been to WDW many times in the past 20 years. In a nutshell, DL is much more convenient than Magic Kingdom. Smaller is better, at least in this case. The feel of DL is more authentic, and the attraction facades are more realistic to the theme of the attraction. DL's Fantasyland also has more attractions than MK.
Having said that, DL CM's can't hold a candle to WDW CM's. Most of them did not have a clue about show times, parade times, where to find characters, or even which characters would be in the park on a particular day. They were rushed and indifferent to most of the questions I had. I even went up to a CM who had a "Ask me about characters button" on his shirt, and all he could tell me was to go to the "toon finder" on the other side of the park and ask him. That would never happen in WDW. The cashiers in the gift shops at WDW are more informed than the people at DL's Guest Services, and if they couldn't answer your question, they would be on the phone in a jiffy to get the info you needed.
If you have little ones who love the characters, MK handles this much better, with clearly defined lines and attentive handlers. In DL, it is a free-for-all with people pushing past others to get their child up front. The DL handlers might just as well be out to lunch.
Another problem that, although increasing in both parks, seems more prevalent at DL is cell phone use/abuse. Cell phones were constantly ringing in the middle of a performance or ride.
One other thing, many WDW people complain about the size of Sleeping Beauty's Castle, but I much prefer it to MK's. There is a real fairytale feel about it that is lost In MK's Cinderella's Castle. I'll never forget how disappointed I was on my first entering Cinderella's Castle 20 years ago and finding there was nothing inside. Reading the Sleeping Beauty tale to my daughter while viewing the dioramas in the castle was a wonderful experience.
You really need to experience both parks, as they are unique. I know WDW will be a more frequent destination for us because we live on the East Coast, but I loved DL and hope to return again. I just hope by then Management can instill a sense of pride and helpfulness in their CMs.