Well, sync, despite its flaws.
See, I prefer to use a tablet for my lemmy use, just like I did for reddit.
And when you're on a tablet, a single column feed is just a waste of space. Double column in portrait is just smoother and more efficient for both scrolling and reading posts. Triple column works better in landscape, but if you comment as much as I do, typing is easier on a tablet in portrait.
So, even if an app is better in other ways, the only apps so far that have multi column views are the ones that used to be reddit apps: boost, sync, and eternity.
Of those, sync is the better visually. More room between cards, better theming options in terms of visibility of cards vs background, etc. So I'll keep using it until it breaks entirely, then likely switch to eternity until it breaks. Boost's column view isn't good for scrolling text posts, though it's better for images only. way too little space in between cards, less flexibility in theming too.
It is the killer feature for me.