Which signal is better between c card and s card in Cambodia?

Cannot compare. Cambodia’s C card and S card are SIM cards provided by two different telecom operators. The quality of the signal depends on many factors, including the operator's network coverage, base station distribution, network equipment quality, etc. It's impossible to say for sure that the signal quality of C card is better than that of S card, because it depends on the specific location and the actual network conditions of the operator.