I have ridden both WDWs and DLs numerous times. I love the ride, but have pros and cons to both.
WDWs- I think it's a better ride experience, but I hate getting in and out of the cars. Of course, if you go to DL, you get a similar folding yourself in and out of the car experience if you ride the Matterhorn. There are some Disneyland people that have insisted to me that their Matterhorn is WDWs Space Mountain, just with different theming. Kind of like Indy vs. Dinosaur. I haven't found anything to confirm this beyond noting some similarities. The only time I ever felt any kind of back or neck issues was when I rode right after a bad car accident.
DLs- It's a much smoother ride, which equates to "not as much fun" in my mind. Still, I really like it and it's much easier getting in and out of the ride vehicles.
The queues to both are different. I think I prefer WDWs because there's more of a build up in my opinion, but maybe it's because there's also that nostalgia from being a kid and being a bit anxious and excited the first time we went through the queue.