My all-time favorite Disney Scene from ANY Disney Film is Crash the Wedding! I just love it SO much! Vanessa is so beautiful and I just love the way the animals attack her, I bet the animators had a lot of fun with this scene. A beautiful woman getting attacked like this :P But also, it's a very important scene in the movie as Ariel and Eric doesn't get to kiss in time and Ursula wins.
^That's the guy's knee. He was genuflecting. It was not an erection.
As far as my favorite scene in the movie, I really can't give a favorite. Even ignoring that the film has a huge connection to my childhood, Toy Story ruined my ability to have favorites. That being said, I actually do have a soft spot to Part of Your World, and the end wedding (a bit bittersweet, really, as that was the last time Disney actually depicted a Christian wedding in an Animated Feature until Princess and the Frog, and it's not even clear Tiana and Naveen were even sincere regarding the Christian ceremony since they technically married before that when they were frogs. Starting with Beauty and the Beast, they either skipped over weddings entirely or otherwise just saved it for the sequels. I also especially appreciate it that Ariel's version of the Royal Weddings stories actually DOES try to emulate actual Christian weddings even more than the actual film itself, it being on a boat instead of inside a church aside, and even THAT was somewhat understandable since there's no way Ariel's family can attend if it was in a land-locked Church. I'm pretty sure Eric got the Holy See's permission before doing that, though.).
Part of that World is easily an iconic scene in Disney Film history that I find as my favorite, but I am also deeply impressed with how they accomplised the who Poor Unfortunate Souls, Paying Deal, and Transformation scene involving Ursula. The effort into making such a scene given the even darker and gory Book counterpart version it is an amazing how Disney accomplish it.
I'm torn between Part of your World and Poor Unfortunate Souls. (The fact that they are both songs is merely coincidence). Part of Your World was memorable, and I'm sure anyone who's seen it has memorized it. But Poor Unfortunate Souls was also amazing and memorable in its own way. (The animation on both was amazing!)