Silica. Wicks moderately well. Does not short the coil. Many people say it mutes flavor, but I have not found this. Flavor with different wicks is just different. Dry burnable many times. Various types available, but I have not used many of them. Some people have been concerned about silica particles being inhaled and harmful. I don't believe this to be the case.
SS mesh. Wicks well when tightly rolled. The finer the mesh the better it wicks, no matter what juice used. Will short the coil if the wick is not insulated like in the RSST RBA. Dry burnable, but I don't do this because of possible health concern. I take the wick out and wash/scrub it to clean. I'm the only person I know who does this. Last a long time.
Cotton. Wicks very well. Does not short coils. Can not be dry burned so needs to be changed often. A lot of people boil in water before using for health reasons. Many different types.
Can't think of anything else at the moment.