Card counting systems in blackjack vary in effectiveness based on complexity and accuracy. The Hi-Lo system is popular for its balance of simplicity and effectiveness, ideal for beginners. The KO system simplifies this further but is less accurate, especially in multi-deck games. More advanced systems like Zen Count, Omega II, and Wong Halves offer greater precision, particularly in multi-deck games, but require higher skill and concentration. While simpler systems are easier to use, advanced systems provide a stronger edge at the cost of increased complexity and mental effort.