The IETF Integrated Service Working Group has specified two service classes: guaranteed quality (GQ) service and controlled load (CL) service. What concerns service subscribers and providers most is the cost of these two services and their performance. For service subscribers, the question is which application deserves which service. For service providers, the question is how to charge their users reasonably to obtain the maximum revenue and what kinds of mechanisms can achieve better resource utilization. We try to answer the above questions under conservative and well-performed admission control schemes, respectively. Simulation results based on the common models of traffic, signaling protocol, policer, classifier, and packet scheduler are presented. When the traffic burstiness increases, the cost difference between GQ and CL increases significantly but the average performances do not have much difference. Thus, subscribers are suggested to use the CL service when the traffic burstiness is high and the delay bound is not critical, and vice versa. For providers, a well-performed admission control scheme is important, especially when the traffic burstiness is high, in limiting the cost difference between GQ and CL. It is observed that, with well-performed admission control, the cost difference can be reduced from 20 times to 1.41 times and 8 times to 1.14 times for bursty and less-bursty traffic, respectively.