Knowing the crucial importance of a service selection, and given the competition between service providers, considerable opportunities are offered for customers to find the best telco service with best pricing. However it took time for customers to manage and analyze the different service data to make the right decision because of the expansion of service providers' infrastructures towards networks providing 3G/4G services and soon 5G services. Several approaches have been proposed to solve the service selection problem, including Multi-Criteria Decision Making (MCDM) methods. We propose in this paper, a MCDM method called MAUT (Multi-criteria value functions or multi-attribute utility theory), which enables the user to choose from among a number of available choices. Our approach is about setting up a Service Broker to look for the best service in order to satisfy and ensure customer loyalty in all-IP next generation networks. An effort is made to manage the different concerns. Service Level Agreement (SLA) ontology process is also proposed to provide users with a clear model when proposals and alternative proposals are sent between stakeholders. Based on MAUT, we present an algorithm to select the best service offered by a service provider. This method is based on utility functions representing the user satisfaction degree.