I think you need to look carefully. They could have multiple sources, and you'll need to check the label and know what to look for.
All Alcon MPS contains polyquaterium-1, including the house brands. Alcon added another preservative, whose brand name escapes me, but I don't think it was used in their house brands. B&L uses polyhexamethylene Biguanide, as does AMO.
Here's an interesting piece on preservatives/disinfectants: