Oh how I love my Disney....we are WDW frequent visitors and Vets BUT we LOVE DL!! Maybe it's because we have not been there as often so it seems fresher to us. I love ANimal Kingdom and some of the shows at HStudios, but California Adventure has the AWESOME Aladdin show. Do you hAve kids? I think with younger children DL is much more manageable and enjoyable. Everything is so close together. It's easy and quick to take mid day pool or nap breaks. We rarely take those breaks at WDW because it seems we spend more time traveling back to resort then have no time to actually rest before heading back. You can MOSTLY stay in a bubble in DL if you stay onsite but it is much harder because Anaheim is literally a step away. The onsite hotels are pricy at DLR , WDW gives you more price options. However DLR has many offsite hotels that are less expensive and sometimes closer than onsite hotels. I LOVE going thru bag check once and being able to hop to the other park in about 5 minutes total. The counter service restaurants in DL are far better than their WDW counterparts. I like Halloween party at WDW better but DL does season overlays on some of their rides which are incredible. I agree with a few of the previous posters, I could easily have done MORE than 3-4 days at DLR ...in fact our best trips are usually 5-7 days and we NEVER get bored. Paper fast passes are still available in DLR which is great but I do miss the convenience of a Magic Bands for room keys and to charge items to room. It's nice that DL has so many nooks and corners to explore but those narrow passageways can make it difficult on busy crowded days. WDW has more room to spread out crowds(as does California Adventure). Photo pass is still only $69 at DL which is nice (I think WDW is up to 169-199). You can still find random surprise characters at DL. Carsland is the best themed area of any of Disneys US parks! I guess it depends on what your looking for and your time, expenses and travel party. Both are great vacations! I agree that WDW is more of a resort that has SO much to do, however I always feel the need (personally) to pack in as much as I can, and need a vacation from my vacation-my Disney marathon. At DL I feel in 7 days, I can DO most of what I want, and still take leisurely meals, pool time, a movie, people watching etc. IN DL I feel like can do it all BUT still come back relaxed, which for me is so not like my other trips. And you don't have to plan as much in advance. Dinning reservations can be made almost up to the last minute and there is no FP+ at DL , so you don't need to plan rides 60days out.
All this being said, in 5 days I'm off for a crazy hot jam packed Star Wars Weekend events at Hollywood Studios and the 24hr event. There will be little sleep and lots of running around , but i will still love every second of it. I am also hoping to get to DL later in the summer or fall, to experience their 60th Anniversary celebrations...this is a great time for someone to try out DL!!
Whichever resort you choose, you will have a wonderful , magical, vacation!