It's still too early to give an opinion, until yesterday I had only used Damus. I think Plebstr is very accessible and from what I saw Amethyst contains a lot of info, stats

Plebstr is sober and uncluttered. Amethyst is a little fancier. I use both OSes and switching UIs is nice too

nostr:npub1plstrz6dhu8q4fq0e4rjpxe2fxe5x87y2w6xpm70gh9qh5tt66kqkgkx8j client is really nice !

without much hindsight, I'd say Damus on iOS but when I switch back to android I think I'll choose Amethyst nostr:note1uvr672yz2eawlt7l5jujvm9wdj54qthcqsud5rgxmty2qfj7w9rsjamrt0