Class ABC extinguishers are effective against Class A, B and C fires, and are required by most fire codes. They are the best overall extinguisher for most common home and workplace environments. If you face unusual threats such as large quantities of flammable liquids or flammable metals you should select a different extinguisher - go back to the By Class page and select one of those classes.
If you are tyring to protect delicate electronic equipment, delicate machinery etc. from Class A, B, and C threats and releasing an abrasive and potentially corrosive dry chemical residue would present a problem, you should select one of the "clean agents" below, Halotron I or CleanGuard which discharge as liquids and quickly evaporate.