As far as filters go, the amount of usage along with the operating environment are often the two greatest factors. I had a bakery A/C unit in which I could not keep the evaporator coil clean (the evaporator is protected by the filter) in spite of a number of different interventions on my part. Having said that, such an environment is unlikely in a commercial building. From my experience, I will always recommend a pleated filter over a fiberglass throw-away filter. At TMC, we install a minimum of a Merv 8 pleated filter. This filter performs well for the money and will not overstress the unit. (Note: some of the best performing filters in the market can also limit the amount of airflow through the unit causing undue stress on the unit.) Filter change intervals depend on particles in air, amount of outside air coming in, etc. As you would expect, a unit with a lot of run time will need filter changes more frequently. Usually, quarterly maintenance is sufficient in most commercial applications.