What really sets them apart
Two payment models
This is the first real difference. Real-Debrid has you buy access in day packs, with loyalty points that reward repeat purchases. AllDebrid, on the other hand, offers a recurring monthly subscription at €2.99, alongside one-off purchases by duration. One asks you to top up, the other runs on its own.
Very similar feature sets
At their core, the two services are alike: torrents and magnet links, Plex/Kodi-compatible streaming, a mobile app, a browser extension, an API. AllDebrid lists 90 file hosts; Real-Debrid covers an even wider catalogue. For most use cases, either one gets the job done.
Where World-Debrid stands out
World-Debrid also offers torrents (as a premium option) and direct on-site streaming, but that's not where it makes the difference. Its real strength comes down to three levers: price (€2.39/mo, below AllDebrid's €2.99), a real free plan with no sign-up, and a cache that instantly serves links that have already been debridded. For classic links (1Fichier, RapidGator, Turbobit), that trio is more than enough.
The verdict
If you want the most mature Plex/Kodi integration, a mobile app and the largest file-host catalogue, Real-Debrid and AllDebrid fight for first place, the choice coming down to whichever payment model suits you. If your need is simply debridding at the best price (torrents included on premium), World-Debrid becomes the most rational option.