The issue I found with Barnstormer is the shared lap bar. I'm a slender human. But, there was enough of a gap between my lap and my oldest's when he was 2 that he still refuses to ride the Barnstormer to this day. He rode just about everything else during our last trip, when he was 8. He did not like the Mine Train. Maybe because he didn't feel as secure swinging back and forth. But he enjoyed Thunder Mountain, Space Mountain, Slinky Dog Dash, and Expedition Everest. He LOVES Soarin, Test Track, and Flights of Passage, so he's decided that Epcot and Animal Kingdom are his favorite parks.
Slinky Dog is very smooth. It may feel a little faster, but it doesn't jerk you around.
Do not make my mistake and shift to Mission:SPACE if Test Track is closed. I did that with my daughter, when she was 4, and she wouldn't even get on. Then she wouldn't try anything that looked even remotely "scary" until our very last day at the Animal Kingdom, when she pointed to the distance and said, "I want to ride that mountain." So I took her on Expedition Everest as her first rollercoaster, and while she didn't want to go on it again, she wasn't traumatized.
So anyway....I would do Test Track first.....then Soarin and go from there.