Voyager is definitely the most polished and great for those who used Apollo for Reddit. It is also very actively developed. For the Android users who do not mind the iOS aesthetic, Voyager is one of the few Lemmy clients on F-Droid.
Thunder is also a great option. I personally prefer its UX more than Voyager, but it is not quite as polished.
I used Thunder for a long time, but I have been giving Arctic a try lately and like it. I will likely give Mlem another shot after the next update. Voyager is another great one, but I have not used it for a while.
Overall, there are a lot of great Lemmy apps and I love that most of them did not get abandoned after the initial wave from the Reddit exodus died down. I think we have more high-quality Lemmy apps than there were for Reddit.