A comparison page where the author's own app wins every category is an advertisement. Here is where I'd honestly send you.
You've never tried anything and your library is a mess
Open Photos, go to Albums, scroll to Utilities, and run Duplicates. It's free, it's already there, and it may clear enough that you stop reading this page. Give it time on a big library.
You only want help choosing between similar shots, and you want to pay nothing
Photoscope, if you're on iOS 26. It has no in-app purchases of any kind, it's on-device, and it does that one job. Keepworthy's picking is free too, but I'm not going to pretend $0 with no purchases in the app isn't a clean answer.
You want to sort photos into albums, fast, by hand
Slidebox. That's what it's built for and it's been doing it for years. Confirm the price inside the app before you buy, because the listing shows several.
You want one app for photos, email, contacts and the rest
Keepworthy doesn't do any of that and won't. Cleanup or CleanMy®Phone cover that ground. If you go with Cleanup, find the $29.99 annual plan rather than taking the weekly default. One caution: iOS has no Recently Deleted for contacts, so a contact merge that goes wrong doesn't come back.
Your storage problem is videos
This is the one I'd argue for. Keepworthy groups near-duplicate videos, plays two of them lined up to the same second, and after compressing one it measures the copy against the original and shows the number. I haven't found another app that does the last part.
You've deleted something you wanted before, and you're wary now
Also Keepworthy, and that's the reason it exists. Every frame in a group is on screen, the pick carries its reason, the ones it passed over carry theirs, nothing moves without your confirmation, and everything lands in Recently Deleted for 30 days.
You have a Mac and want to do this on a real screen
None of the big apps above has a Mac app at all. Keepworthy does, on the same purchase. Two very small apps also pair, Tide & Keep and Culpix, if you'd rather try something with a handful of ratings than something with none. If the Mac is all you care about, PhotoSweeper at $14.99 and PowerPhotos at $39.95 are long-established and good. Check the pairing before you buy: PhotoSweeper's iPhone app is a separate product on its own subscription, so owning the Mac one gets you nothing on the phone.