When comparing Greenify vs Wally, the Slant community recommends Wally for most people. In the question“What are the best Material Design apps?” Wally is ranked 32nd while Greenify is ranked 49th. The most important reason people chose Wally is:
The app allows searching for wallpapers by text and tags as well as allows filtering them by categories, resolution, and/or aspect ratio.
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Pros
Pro Even works without ROOT
Greenify even offers battery savings to non ROOT devices, though it may be limited compared to what can be done with ROOT and Xposed.
Pro Hibernates, instead of freezing apps
Greenify's mane function is to hibernate any installed apps. This allows users to to quell overly active apps that are draining their battery without having to delete them. This can be done with or without ROOT.
Pro Lots of different ways to find wallpapers
The app allows searching for wallpapers by text and tags as well as allows filtering them by categories, resolution, and/or aspect ratio.
Pro Has a huge selection of high quality wallpapers that's constantly updated
The app uses wallhaven.cc as the source for wallpapers. Wallhaven.cc, the successor of wallbase.cc, is a vast resource for high quality wallpapers.
Cons
Con Greenifying without ROOT has to be done manually each time
When using Greenify without ROOT access to hibernate apps, it has to be done manually each time. There is a widget and shortcut that users can set to their home screen to make this action a bit easier though.
Con app not available in play store
Con Buggy
Multiple people are reporting that the app can sometimes crash or crash the launcher or not work properly in some other way.