Jerboa is the official Lemmy app created by the Lemmy developers. It's unfortunately not a super great experience at the moment, but it's improving quickly with all the attention on the fediverse. I use the mobile site as a PWA, but I keep Jerboa installed and try it every now and then. I'll make the switch permanent soon, I'm sure, given the rapid development.
Edit: Forgot to mention it's available both on F-Droid and Google Play, in case you avoid Google services on your device.
Jerboa isn't the worst experience. I'm using it now and much more forgiving of some of the ui weirdness because I like it and want it to succeed unlike Reddit. Plus I can understand stability issues considering .... [gestures at everything]
I'd like to add that Thunder seems so be an up and coming and very promising looking app for Android and iOS. I've used it a little and it seems very nice. It's available on izzyOnDroid or their github