As migration from 4G network to 5G network gains momentum across the world, network operators are faced with different options when migrating from the 4G to a unified 5G network. These options have been broadly classified as standalone (SA) and non-standalone (NSA) options. While an operator can migrate from the 4G network to the 5G network in one step, using the SA 5G deployment option, for most network operators, the migration from the 4G network to a unified 5G network is a multistage process, starting with an NSA 5G deployment option. This paper investigates network selection decisions for a mixed deployment of NSA and SA 5G network, along the migration path to the realization of a unified 5G network. To the best of our knowledge, this is the first paper investigating network selection decisions in a 5G network with mixed deployment of NSA and SA options. A Markov model has been developed to investigate the blocking of MBB, eMBB, and uRLLC services from different categories of users in the network, based on their equipment capabilities and service subscription profiles. Moreover, the developed model has been used to investigate the effect of users’ equipment capability on average utilization of the heterogeneous network. Simulation results show that users’ equipment capability and users’ service subscription profiles significantly affect service blocking probabilities and average utilization in the heterogenous network. The study underscores the importance of upgrading users’ equipment and users’ subscription profiles before reaping the connection-level QoS benefit of deploying the 5G network.