Sync is more polished, but Infinity has a much better layout on the Galaxy Fold. I’m using Infinity for now, but hoping it improves quickly.
Neither is as good as Reddit Is Fun for foldables, unfortunately. That had a perfect interface IMO. Much better than Apollo too.
One thing that really bothers me on Infinity is that I see no way to show the parent of a comment that I am looking at. It only times you the option to show all other comments, but not the parent specifically.