Electronic air filters are excellent and work very well provided they are monitored and cleaned regularly. If they are cleaned regularly, they will work at about 95 percent efficiency. If they are not cleaned regularly, their air-cleaning capacity is reduced rapidly. HEPA filters are the best nonelectronic disposable filters. They are expensive, but good enough to use in hospitals.
Electrostatic filters are also good.
Last, there are ordinary pleated filters and the standard furnace filter that protects the furnace but does not clean the air.