I rode WDW SM last September and DL SM in April
With regards to DL-SM - WOW! It was amazing. I have always liked DLs a bit better than WDW but the improvements put it miles ahead.
It is hard to explain the difference - WDW is single file seating (Like the Matterhorn at DL) while DL is two across. This makes DL a bit more comfortable and easier to load and unload.
The lift hill at DL has multiple phases. I only rode it once in April but you would go up a ways in a tunnel with one type of effect and then go flat for a bit around a corner and then up another lift with a different effect and the effects were stunning.
The ride itself seemed smoother and a bit wilder at DL. Also the ride seemed darker and a much better job was done of hiding the ride structure. My niece described WDW SM as riding a roller coaster at night. You could very much tell you were on a roller coaster, you could make out the track, supports etc. At DL we were far less conscious of the ride structure, layout etc. This also made turns and dips more surprising, because they were less obvious until you were into them.
The end is somewhat similar, they both have similar effects in the braking tunnel.
DLs new Space Mountain is great, it would take a lot of work to make WDWs match it, but hopefully they will.
One other neat feature that DLs SM had was the way it handled handicapped access. Right in front of the standard loading station was a transfer track. Don't know if I can describe this well or not, but it was two parallel tracks that slide sideways. So if a train was on this piece of track, it could shift to the side. The track and the train could shift to the left with a new piece of track in its place. So they would bring a train onto this track, slide it to the left into a special boarding area. This is where handicapped riders could board. While the one train was there, other trains could continue to load and be disbatched going over the other piece of track. This let handicapped riders load at their own pace, no rush and no one was held up. Once the train was loaded, they shifted the track to bring the side train back on the main track and send it off. When it returned to the station, they did the same thing to unload it. It kept the trains moving, but gave extra loading and unloading times to folks who needed it. It was very well designed.
