I tend to support at RfA; being a sysop is (and becoming one should be) no big deal, so if I feel I have nothing new or productive to add, I will sooner not take part than oppose. While having the sysop bit is indeed no big deal, having sysops is important for the project, so below are some rough criteria for evaluating and participating at RfA.
I endeavor to only ask questions that would genuinely be helpful or useful to me and other participants, sometimes waiting until after the initial questions and participation. RfA is a discussion seeking a consensus, so I try to provide thorough and meaningful explanations when appropriate, especially if I oppose. Regardless, I try to follow and stay actively engaged in the full process, commenting when productive.