The optical emission characteristics of Atmospheric Pressure Guided Streamers (APGSs) generated in He and Ar mixtures with N2 and O2, are herein reported. The reactor employed is based on a DBD geometry and driven by high voltage microsecond positive pulses. For fixed values of the main operating parameters, the influence of the gas composition on the formation of principal emissive species as well as on the rotational temperature of probe molecules is investigated. In addition, the vibrational temperature is estimated for both He and Ar mixtures. Optimal gas compositions for enhanced plasma chemistry are found. This is of great importance in various applications and especially biomedical ones. In the latter case the temperature must be maintained close to the room one.