My first comparison: the celebration show this year, Magic, Memories and You. This show in general is a feat of technology, no matter which park it is seen in and the score always brings a smile to my face. In Walt Disney World, the show is projected on the castle while in Disneyland it is projected on the facade of 'it's a small world'.
Being projected on surfaces of two very different sizes and shapes gives different perspectives to the shows, even though they are relatively the same show. The part of the show where 'it's a small world' plays and the dolls come marching across the building visually makes more sense on the 'small world' facade (naturally) while the scene with the rocket blasting off looks so much cooler on the castle as a tower launching off of the castle.
If you are set on looking for your picture to be in the show, you will have a better chance at that if you are watching the show in Disneyland. The closeness and size of the 'it's a small world' building makes it much easier to spot the pictures, unlike on the castle where the pictures tend to be smaller and harder to see.
So, which one is better? I honestly could not decide. They are both beautiful and have their own highlights. So, I am leaving it up to you to decide. Here are the two videos I took of each show, watch them and leave me a comment letting me know what you think! I would love to hear your thoughts!