What is the best SNES emulation app for android?

Either snes9x standalone app or the snes9x core in RetroArch. Dealers choice. If you just want to play SNES, go for the standalone app. If you're looking to get more into emulation as a whole or you want RetroAchievements, get RetroArch.

What’s the difference between the different codes on retro arch? I’m using the bsnesx accuracy, whatever that means.
- For bsnes, accurate uses more resources to emulate more accurately. Some emulators aren't as accurate. They aren't exactly 1-to-1 compared to SNES. That doesn't mean they perform worse. In fact, it often means they perform better. But running better (or different in any way) means it's a less accurate emulation. The other versions of bsnes and snes9x are less accurate emulators, but require less resources.
  
  From a practical standpoint, I'm not sure you'd even notice the difference between any of them. Snes9x takes significantly less resources than bsnes though. Unless accuracy is what you care about snes9x is the better option.

Heads up since everyone is recommending Retroarch:

Retroarch has a SIGNIFICANT learning curve. There are so many settings hidden in menus and submenus. I recommend looking up some YouTube videos before diving in if you're a fist-timer, since it can get overwhelming really quickly.

If I may add a counter-argument. I avoided RetroArch for years due to this, but it is only partially true. If you are even a little bit proficient in using a computer, it will feel slightly finicky, but once you have it setup, it is pretty easy. Many things in emulation or hacking are much more complicated. I now use Retroarch daily and feel kind of stupid for avoiding it.
Use Dig as a front end to retro arch and you never have to worry about it. Of course since android 12, setting up dig has had its own mess wrt scoped storage and such

Retroarch, hands down :) Any core will do fairly well, S22 is quite capable. I love the retro-achievements functionality, ir adds more depths to some games

Retroarch. And if you want it to look a bit prettier use daijisho as your launcher.

https://retrogamecorps.com/2022/03/13/android-emulation-starter-guide/

Is there a bsnes/higan core for retroarch on Android?
- If I remember correctly, yes. But I can't tell you how well it runs. I use Snes9x usually on the Anbernic RG405M and occasionally bsnes-hd for wide-screen hacks on the Retroid Pocket 3 plus
  
  The play store version is a bit outdated though. Use the APK from the retroarch homepage and choose your cores with the internal core downloader.

I use Lemuroid, an open source front end for RetroArch. It is dead simple to use, just point it to the ROMs folder on your phone, tap the game you want to play, and it all just works!

I've installed Lemuroid this morning. It is the only open source SNES emulation app that is available un F-Droid. I haven't usted yet, but i'll give it a good chance 👌🏻
I've used Lemuroid for Game Boy emulation before but it had trouble remembering my saves for some reason. It'd sometimes forget that I'd saved recently, and so I'd load and find myself in an earlier save. Also on a Samsung phone, albeit an A-series. Do you know what might have caused this?
- Nope, I haven't had any issues with save states. Keep in mind, there's a difference between saving the state manually and the option to auto save state when you leave the app. If you force quit Lemuroid or whatever goes wrong as you leave the app, the auto state save might not work. That's my best guess. I usually do both, save state myself, and rely on the auto save state. :)

I recommend Lemuroid for most retro emulation, it has a user-friendly interface and it is easy to set up, you basically scan your rom folder and you are ready to go.

RetroArch is also great but the interface is kinda confusing imo, great for technical people I suppose, it has lots of options.

RetroArch with a different front end