Hi Alison!
Thank you for visiting the Disney Parks Moms Panel. You're right;
Na'vi River Journey and
Meet Favorite Disney Pals at Adventurers Outpost are two completely different experiences.
If you asked my youngest daughter, she'd choose Disney characters all day, every day. Na'vi River Journey is a great attraction for young ones in the sense that it's slow, has music, and is visually stunning. However, if your daughter is not a fan of Avatar, then the story won't mean as much to her. Walking around Pandora- The World of Avatar is an incredible experience even if you don't have time to ride.
Some questions to ask yourself are will you see other Disney characters in different parks? Does your daughter love character meet and greets? Have you ridden Na'vi River Journey before?
My 5-year-old daughter has done both, and she'd still choose Adventurers Outpost, because she can't get enough of Mickey Mouse. However if this is your only chance to ride, and your daughter will have opportunities to see characters elsewhere, then I'd choose Na'vi River Journey.
I hope this helps! If you have any other questions, please come back and see us real soon.
Tania