Matter of opinion, of course.
That being said, connect is pretty much the best looking, and has been perfect in reliability for me.
Summit is equally reliable, but lacks in the ui department.
Eternity has a single killer feature, the ability to have double columns in portrait mode which makes it better on tablets, and has a good ui otherwise, but can be spotty with crashes gets and there.
Thunder is another that's got double columns as an option, but it hates me and my devices. Almost impossible to log in, which is a major problem for me, but it isn't something I've seen anyone else have happen. Great app overall, it's just a fail for me in specific. The rest of the ui, though, kinda limited in options, but works fine.
That are the open source options that I've kept using after the initial boom of apps for lemmy. I have jerboa on a couple of devices, but it lacks a ton of features for my preferences, so it doesn't stand out other than in reliability.
Lemmy is one of those cases where I keep hoping someone will do an app the way I want, but it'll never happen because there just aren't enough users with my use case. Tablet centric, dyslexic, old eyes, and a dislike of oled black themes. So I end up using sync more than anything else because the dual column layout is perfect, and I can fiddle with things enough to get near optimum contrasts between text, "cards", and background, so that I can actually see what I'm doing and not have to fuck around trying to get around my issues instead of just enjoying lemmy.
If connect had dual column, it would be my main app of choice, though. It's what I use on my phone, since one of the themes does work fairly well for me in that screen format.