Epcot! It was my kids' favorite park starting at 2 years old. (At 9, there's a chance that DHS edged out for my eldest, but he still loves Epcot).
AK was a flop for us on 3 of our trips, so we finally skipped it our last trip. We're trying half a day there this time. I do think AK is worth trying for a first-timer who has at least 4 days, but not for 2. We actually find AK the hardest park to move around in. Even when it's not super crowded, the paths can get crowded. My kids like HS, but it had the third favorite spot for a while - only getting out of that recently at 9 years old for my eldest. Epcot was still his favorite at 8 though.