WDW is an immense resort. Emphasis on the word resort. 4 theme parks, 2 water parks, plenty of extras like boating, fishing, golfing, swimming, and so many choices for hotels and restaurants. We typically walk approx. 7-10 miles a day when we are there. It takes probably 7 days to do it right. Epcot is worth the price of admission. I've always said though if they would have built Epcot at DL then I wouldn't go back to WDW. I love Epcot that much.
DL is so much smaller, quaint, nostalgic, and unique. It was built by a father for his family while WDW was built for the masses. I love that you can step off one attraction at DL and a few steps away is the next. Not the case at WDW.
Pirates, Space, All of Fantasyland, Aladdin, IASM, Autotopia, Fantasmic!, RDCT and Indy are all better at DL.
The Jungle Cruise trees and plants all seem more lush to me. Is it just me? It seems to completely surround you at DL and not at WDW. What I really like about DL is California in general. I love being able to visit Monterey, SF, Yosemite, and San Diego and bundling it together into one big trip. I love the Hotel Del Coronado in San Diego. I love the Pacific Coast Highway and driving it up and down the coast. The weather is always amazing. No humidity.
Splash, Epcot, Big Thunder, ToT, Restaurants, Resort Hotels, and did I mention Epcot?

Have fun planning to me thats a huge part of the fun of going on vacation. We do countdowns on dry erase boards in the kitchen.