This Macstories article by Ryan Christoffel is a treasure trove of "shelf" apps for iPad Pro and iOS 11. They've done most of the heavy lifting and I benefit from a lax publishing schedule.
I mostly agree with Ryan's choices but I think we have different needs. I prefer Dropped over the other options. Read Ryan's review for context. I'll add a few additional comments here.
I don't like Scrawl Pouch because it fails at what makes iOS 11 Drag and Drop great. An object in iOS 11 isn't just one thing. If you drag an image out of Safari it's an image drop but it's also a URL. To Scrawl Pouch it's just an image. I like Dropped. It looks nice and gives me access to the rest of the object properties. I also really like The Shelf but found the drag to delete a bit tedious.
A use case that I think is pretty common is dragging an image out of a YouTube list view. Dropped and The Shelf capture the image but they also hold onto the URL, which is really what I care about.
These "shelf" apps are one of the best pieces of iOS 11 in my book. The system has long lacked a good clipboard history and these few new comers are very promising, even if they aren't feature complete yet.
I have hindsight on my side though. Today Copied 3 was released and this is my preferred way to hold onto clipping with iOS. I've raved about Copied over the years so regular readers shouldn't be surprised.
Copied 3 adds support for Drag and Drop in iOS 11. It also syncs with my other devices through iCloud. I like the multiple named groups in Copied and use them extensively. I can name clippings and search works like a treat. The only thing Copied 3 is missing is support for a broad range of document types. Dropped supports PDFs and other object types. Copied does not.
These are early days for Drag and Drop and I'm excited to see where this leads. I'm surprised Apple hasn't provided their own solution but then again, it's still a gap on macOS too. The real question for iOS: is there any money in the App Store for utility apps that solve problems Apple doesn't. I sure hope so.