I would have to say small world and peter pan are tied for first in my eyes. It's difficult to compare attractions so vastly different. I think thats one reason I love disney. It's one thing to go to a Six Flags or Cedar Fair park and pick out a favorite coaster because, even though different configurations, they are all coasters with the same basis for excitement. But then you go to Disney and it's even difficult to pick a favorite ride in each area let alone an entire park. For me, it's hard to pick Space Mountain over COP, or Pirates over Haunted Mansion, or in this case Peter Pan over Samll World (for just a few examples) because I can honestly say I like them equally but for completely different reasons. Or as another example, is it no very difficult to choose your favorite past attraction for the very same reason.
In this case Peter Pan is great because it is a classic example of less is more. That simplicity can be as effective as insanely complex. How a minuture London can make you feel like you are actually flying over it, or a few set pieces and a little black light paint can really make you feel like you are in another world with peter and the gang.
Now, as far as small world, I was never a fan until the remodel. I haven't had the pleasure of an actual visit just yet, but I've seen the footage and it's impressive. I'm truely captivated by how spectacularly elaborate and visually impressive this ride is.