what lemmy app do you recommend and why?

I'm biased because I chat a lot with the developers, but I'd highly recommend Thunder - very sleek, very customizable, VERY nice compact mode, and a very welcoming group of people. If you try it and feel like something big is missing, they're quite responsive on github! Been quite impressed with the leaps they've made with features on every release.
- Thunder is a great mix of functions and UI. The compact mode is really great.
- I second Thunder. Only a few minor gripes from me but switching from sync (gross ads) has been just fine
- Thunder does look quite nice, but sadly my long defunct keyboard app doesn't work with it, and they weren't able to get the apk to test a fix for it. (But they did try.) You'd think, of all things, a keyboard and input field wouldn't have compatibility issues, but I guess that's Android for ya.
  
  Oh, that's a bummer :( what happens when you try to use it?
- Yup. I've configured my thunder to look and feel really similar to the way I had Relay set up. The compact modenis great and the customizability is really good.
- Man I've been using Voyager since the beginning after switching off jerboa but all these thunder comments are making me want to try it out!
  
  Give it a shot! Definitely check the settings if you do, the tweakability is fairly expensive - and if anything feels missing let the team know on GitHub!
- I'd use Thunder more if they had mark as read while scroll, and hide read posts (I think they already have the later) if these requests are outdated please lemme know.
  
  In settings , you can toggle on mark as read on scroll and hide read .
  
  "dismiss read" is an option you can add to the FAB, and mark as read on scroll looks to be a setting now as well! Haven't used either, but hope they meet your expectations :)

I like Sync. It's fast and I find it really easy to use.
- Tried it, immediately uninstalled it after I saw that it has ads.
  
  I'm OK with the ads. The coder didn't put disappointingly many ads. And the few ads I saw weren't annoying. I hope the ad $ has been a 👍 reward for the coder for making and maintaining Sync.
  I <3 the user interface's design. It's Google's design.

Boost, boost have always been my favorite, on Reddit and now Lemmy. Cant say more then i just like it, and like the developer
- I also use Boost because of one nice feature: it highlights new comments in a different color.
  I had to turn that feature on in the settings, and it's very convenient when revisiting an active post.
- Boost here as well, was a RIF user and I've been able to make boost look and feel sorta like RIF which is great.
  
  Yeah, rif was my absolute favourite, and I miss a lot of the features it had. I've been toying with the idea of cloning it for Lemmy, but maybe I'll give boost a try first.

Voyager. It economizes on screen real estate, and has similar (therefore, familiar to me) ergonomics as Relay did back at the old place.
Tight design that stays out of the way, and updates frequently.

Sync, it has a very nice user interface, I've been using it for years (previously for Reddit).
- Same and same.
- Really? We switched away from Reddit because it started forcing everyone to use their crappy, proprietary, ad-infested app, and now we use proprietary, ad-infested Lemmy apps?

Eternity for lemmy is peak user experience imo
- Is Eternity still in development? I don't think there has been a release for 6+ months.
  
  No. The last commit made by the developer was 4 months ago https://github.com/Bazsalanszky/Eternity/commits/master/?author=Bazsalanszky

Thunder because I think it has the most features, the UI is designed pretty well and I like the user experience it offers. They are working on amazing new features like notifications over UnifiedPush and moderation tools (I think no other app has mod tools). It's completely free and open-source and available on F-Droid via the IzzyOnDroid repository. And unlike Sync, it doesn't have ads.
I recently also learned that it's one of the few open-source (and still actively maintained and developed) Lemmy apps, which is quite sad. I don't understand why so many folks use proprietary apps like Litoff, Summit, Connect, Boost or Sync. Sync is especially bad, because it has ads and trackers.
I tried Jerboa before I switched to Thunder and hated it, it just feels like an incomplete and buggy mess with poor UI/UX.

Racoon for Lemmy still have some rough edges, but is really cool and nice looking.
- Second this. I have had some weird freezes with the recent thunder updates so I installed raccoon. It's not as feature-packed as thunder but you can set up enough UN's it's really nice looking.

I use sync because that's what I used to use for Reddit.
- I use Boost for all the same reason. The familiarity made the transition much easier
- Doesn't it have ads?
  
  Yes, but not many and they aren't 'sneaky' pretending to be user posts though. I think I can pay to remove them, which I probably will do eventually.

Jerboa. Because it works alright, it's open source and it's the Lemmy team's app.

Voyager is the way. Only downside is that there is no notifications feature implemented yet.
- Thunder already has notification support, and they are even working on enhanced notifications using UnifiedPush
- I see that as a bonus lol

Thunder

Thunder is nice. I loved Liftoff but that got abandonned, transitioned to Eternity which I came to love even more but that seems to be abandonned as well. Thunder is closest experience I could find to those two.

I use Connect, and I have no complaints.
Tried Jerboa early on, but at the time it was super buggy. Hopefully it's better now - I feel like a FOSS app is a way better option for Lemmy just on principle.

Voyager for iPad because is the exact same experience I had with Apollo for Reddit which was the best Reddit client back then. Boost for Android because, well, is the same as Boost for Reddit which was the best on Android :)

Jerboa
Its simple and lightweight. Can optionally get it on the app store if you want.

Connect.
I like to have posts and comments as small as possible, without large pictures being downloaded before I click the post, and it must have a dark mode.
I also tried Jerboa and Voyager, and while they're also customizable, I couldn't get it exactly right. Maybe it's possible now, but I can't be bothered to keep up to date on three apps when Connect does it just fine.
I'm not sure what any of them look like by default. I basically set out to recreate the way I used RiF for Reddit, which also wasn't the default.
- I've been using Jerboa for that reason. Condensed information so I'm not constantly scrolling.
  What's Connect look like for you?
  
  Posts:

The ol boosteroo! Nice and simple.

Connect. I came from Sync for Reddit and Connect has that nice clean layout that others lack as well as nice, simple swipey gestures.
I've tried pretty much all of the others ones (at least those that existed up to 3-4 months ago) and I keep coming back to Connect.
- Is there a reason you still don't use Sync?
  
  Reddit and Lemmy have a few different nuances that Sync doesn't properly address. A good example is blocking communities or individuals right from the post menu. Syncs development has been sporadic or at least was when I paid attention. In addition Connect has a few additional features like "hide all above" which is a nice feature to have once you get used to it.

Tried a bunch and landed on Thunder. It's minimalist, tucking away all its features nicely. It's experience is like rif if you ever used that, but lots more going on in the Settings menu to set it up how you like.

Jerboa, probably just because I'm used to it

I've tried a large number of apps in search of something to replace multireddits. Summit for Lemmy is the only one which managed to implement this under its multi-community functionality. The app is being consistently updated with new features and I do not feel like I'm missing out on anything other apps offer.

Using Connect. Very simple UI, and works on older phones (Android 5+, while it says 4.4+, it crashes on 4.4).

Looks fine. You have better screen estate, 7.5 posts while I only have 6 posts on a screen.
I think the reason why I changed from Jerboa was the data usage at the time (July last year). It'd download the entire picture instead of thumbnails. Sometimes it lagged.
The reason why I liked RiF was basically only that I had used it so much that I knew where everything was. I've been using Connect long enough that I'm not eager to switch at the moment.