Both apps start the same way: point a phone camera at a card and get an identification back. What happens after that scan is where the two apps stop being interchangeable.
Where Collectr wins
Collectr is built around a polished, organized collection view rather than sports cards specifically, with portfolio value tracking and cross-device sync. If the goal is a clean answer to "what do I own and how is it changing in value," Collectr is built for that question first.
Where CollX wins
CollX's scanner matches against a database of over 17 million cards spanning sports, Pokémon, Magic and Yu-Gi-Oh, and its free tier is a genuinely useful starting point for identifying a box of unsorted cards. CollX Pro adds unlimited collections, CSV export and priority support for a seller who needs to move data out of the app.
What neither replaces
Both apps' valuations are estimates users report can run high or low depending on the card. Treat either app's number as a starting point, not a listing price, and confirm the exact set, number and variant yourself before it goes on eBay.