I’ve spent many days in both parks; here’s my (subjective) comparisons (attractions unique to MK are in bold):
Space Mountain - DL is WAY better; much smoother, better visuals, and music.
Buzz - Main difference is that one has fixed guns on a movable car, the other has movable guns on a fixed car.
Asto Orbitor - WDW is better because it is still up on the raised platform vice on the ground
Autopia/Raceway - Both terrible, but if I had to ride I would choose the DL version; much more interesting layout and nicer landscaping.
Carousel of Progress - Unique to WDW. It’s a classic and must be seen at least once.
Peter Pan - slightly different, but about the same. WDW version loads a bit faster
Mickey’s Philharmagic - Only in MK; it’s a fun 3D movie with typically short lines.
Fairytale Princess Hall - an elaborate meet and greet featuring - you guessed it - princesses.
Winnie the Pooh - Generally similar, but with a different execution. I enjoy them both equally.
Seven Dwarfs Mine Train - The newest “headliner” in the MK, and one of the busiest.
Voyage of the Little Mermaid - Identical to the DCA version, but with a very cool (and long) queue to walk through to get to the ride.
Dumbo - The ride itself is identical (but MK has two of them). The circus-themed queue area is very well done and worth checking out.
Barnstormer - Identical (or almost identical to) to the kiddie coaster in DL’s Toontown, but with different theming.
Casey Jr. Splash Zone - quite elaborate and very wet…
It’s a Small World - The DL version is an order of magnitude better. The MK version is considerably shorter and lacks both the beauty and charm of the original.
Haunted Mansion - The ride itself is essentially identical, although the WDW version may have an additional scene prior to the Séance Room. The interactive queue at the MK is a marked improvement over the DL queue.
Hall of Presidents - In my opinion some of the finest AAs that Disney has ever created. Many consider it boring, I consider it inspirational. a must do at least once.
Riverboat - essentially the same experience, although the MK version is now longer than the DL version (since they cut off half the river to make way for SWGE).
Tom Sawyer Island - hard for me to compare as I haven’t been to the DL version in decades (before the pirate overlay), but what I remember of it, the MK version is larger and has more to do/see.
Country Band Jamboree - If you saw the DL version before it was converted to Pooh, then this show is identical. If you haven’t seen it, it’s a classic with great AAs; everyone needs to see it at least once.
Big Thunder Mountain Railroad - Except for a few slight track differences, it’s essentially an identical experience to the DL version.
Splash Mountain - Conceptually the same, but the MK version is longer and I think more well executed.
Pirates of the Caribbean - Very similar, but I like the DL version better as it has additional show elements and a more cohesive narrative.
Swiss Family Treehouse - This was originally built in '71 as a clone of the DL version. Since the the DL version was converted to a Tarzan theme. Although I think the Tarzan conversion is good, the original is a great nostalgic looks at an early years DL attraction.
Tiki Room - Identical to the DL show, but without the talking tikis (and Dole whips) in the waiting area.
Aladdin’s Flying Carpets - a “spinner” similar to Dumbo but each “carpet” has 2 rows of seats and there are spitting camels.
Jungle Cruise - Conceptually the same, but the MK version is longer, and in my opinion “better” if you factor out the DL “nostalgia” aspects.
I have less than no interest in meet and greets, so I can’t say what the similarities/differences are between the two parks.
What you won’t find in the MK - Snow White’s Scary Adventure, Pinocchio’s Daring Journey, Storybookland Boats, Casey Jr. Train, Matterhorn, Submarine Voyage, Castle walk-through, Roger Rabbit’s Car-Toon Spin (or any of the other Toontown attractions), Explorer Canoes (does DL still run these?), Columbia, Indiana Jones and the Temple of the Forbidden Eye, Great Moments with Mr. Lincoln.
Similar rides in other parks:
Epcot - Soarin’ is identical to the DCA version other than queue theming.
DHS - Star Tours - essentially identical to the DL version (assuming that DL converted to the 3D films) with a more elaborate queue. Tower of Terror is much better than the DCA version had been; haven’t been to DLR since the GotG retheme was complete. Toy Story Mania - the ride is more or less identical to the DCA version, but the queue is much more interesting.
AK - It’s Tough to be a Bug - identical to the DCA version, but the pathway through the roots of the Tree of Life is very pretty, and gives you a chance to appreciate the intricate carvings close up. Primeval Whirl - I mention this because the track is essentially the same as Goofy’s Sky School, but with cars that spin; I like it better than the DCA ride. Dinosaur - Although this is a “unique” ride to WDW, I mention it hear as the ride system/track design is identical to Indiana Jones in DL. Indy is a much better ride than Dinosaur, but the difference in theming makes it worth checking out.
Obviously there are many more attraction unique to WDW in these three parks, but I was focusing on “similar” attractions, per your original post.