For my son, it was Animal Kingdom hands down. He loved AK. So much to do, we easily could have spent two days there. There aren't as many "rides" but as a PP said, many more open ended/exploratory activites that are great for the littles.
We spend about 3 hours in HS and left. It was a miserable failure. We walked out of Disney Junior, walked out of Muppets, couldn't get a reasonable fast pass for TSMM. He did like lights motor action, but that was about it. We'll go back on this upcoming trip for Star Tours and TSMM, but then leave for another park for most of the day.
ETA: My son is shorter than yours, so he couldn't ride ToT. I don't think that makes a big difference though