This paper presents a modular decision flow for the selection of radio access technique (RAT), carrier frequency, and bandwidth for opportunistic networks that are operator governed temporary extensions of mobile communication network infrastructures. In this study the emphasis is placed on finding an optimal (band, RAT) combination for each opportunistic network link so that adequate bit rate can be guaranteed for each user. The proposed algorithm considers realistic spectrum bands, namely, Industrial, Scientific and Medical (ISM), TV, and International Mobile Telecommunications (IMT) bands. The obtained results show that the bandwidth usage at each band can be balanced by using a modular decision flow so that the quality of service (QoS) for each data type is maintained.