Microelectromechanical relays are of great interest in radio-frequency communications, power switching applications, and in automatic test equipment. Ohmic DC relays must maintain low electrical resistance over millions to billions of cycles. As such devices are cycled, soft metal coatings such as gold either tend to (i) cold-weld, causing failure due to adhesion, or (ii) accumulate friction polymer, causing failure due to high contact resistance. Recently, hard, adsorption-resistant conducting metal oxides have been of interest for improving microrelay reliability. However, there is little understanding of their effectiveness in contaminated environments. In this work, we address quantitatively the interplay between materials, environment and contamination. Specifically, we determine the immunity of adsorption-resistant RuO2- coated microrelays relative to catalytically-active Pt-coated microrelays. At high contaminant levels, an optimum choice of both the material and the environment can improve microrelay performance markedly.