I have a 4 year old daughter and 5 year old son and we were there in January and were able to see all of the parades. By far, our favorite was the one at AK because the character interaction in that one was just amazing. We were right up front and both kids got lots of pats on the head, handshakes, waves, etc. They had a great time with it. Our second favorite was the MGM parade because, like everyone else mentioned, there are lots of characters in that parade that you won't see anywhere else. We were right up front once again and got a fair amount of physical character interaction and lots of waves. They had a great time at both parades!
We also saw Share a Dream come true and Spectromagic. We enjoyed them both, but they tend to be more for visual display (in our perception) rather than character interaction. I could tell both kids had more fun at the MGM and AK parades.