I lost my browser link to this great chart someone had created. It was in grid format that showed lists of battle pets that were strong and week versus others. It included double counters where a pet had a strong attack against a pet that had weak attacks.
Also included PvE pets. I think it was hosted in google docs or PasteHtml (which is currently down)
I'm trying to describe it better because what I've searched for isn't it. It was a grid format with each pet family in a row and each in a column. Within each grid square there were colored sections with pet names that fit the strong/weak/double type.
Essentially you could use it to look up a pet you're against and find the "best" pet to use against it.