OurGroceries was definitely the best on Android, so I happily bought two licenses ($5 each, all they do is remove the ads) there years ago. Switching to iOS, buying it here as well was similarly a no-brainer. I just wish iOS got the dark theme as well. So I'll have to shoot off an email to the developer. It's actively but not frequently updated.
The big thing is, OurGroceries has list sync, and they had it when nobody else was considering doing it. At least on Android. I've been using it there for all the six years I've been on that platform. I don't know how long it was on iOS or what features came when. But now that I am on iOS and my wife is still on Android, the sync works just as good as ever.
Another feature we've recently adopted... or rather I have, and it synced to her... is departments. So if I add bread to the list, I leave that alone. But if I put Ibuprofen (i.e. Advil) on the list, that goes to the Pharmacy department. And it's automatic, it remembers the things you add and their department. So if she were to add "headache medicine," that's a new name, and it would go in the default department. Each item name can also have a picture, and/or barcode associated with it. I didn't mess with the barcodes much because barcode scanning in Android was always a PITA. On iOS I'm finding it a lot easier, so I think that's something I'll do on my end with the iPhone, and that info will sync on over.
The web feature is good, too. Basically you just go to their website and sign in with the list owner's username and password, and you can use the app on the site, and it syncs up just as fast. My wife's always asking if there's anything we need at the store, and if so to "put it on OurGroceries." And I can easily do that on my phone, but I keep it bookmarked on the desktop as well. So if I'm already parked at the computer, it's slightly easier to use that than to bother with my phone.
I've now paid $15 for OurGroceries. If for some reason I switch to Windows Phone, I'll happily buy it there as well. I can't think of a higher endorsement than that. It's not that it's worth $5 to get rid of the ads. It's just a banner, one line of text. It's more that I'm happy to pay the developer for their work.