Cardano's consensus protocol is PoS, and ZILLIQA uses pBFT. The two agreed protocols operate under different threat models. PoS assumes a cryptoeconomic model where the adversary does not wish to lose the pledge in order to embody his malicious interests. On the other hand, pBFT suggests a more severe threat model, where miners are Byzantine and may maliciously deviate from the execution of the protocol. Another advantage that pBFT has over PoS is completeness - this means that transactions in ZILLIQA do not need to be acknowledged. I would prefer ZILLIQA.