I love the Harry Potter Universe and I am no big fan of the Avatar movies.
I watched the first one after we came back from our vacation in 2017.
But given the choice, I would ride Flight of Passage anytime.
Not a fan of Avatar (or HP to be fair).
Its rare for me pick anything Disney over Universal, but FOP is very impressive IMO.
Gringotts is OK - but once per trip is more than enough for me unless its a walk on..