Are new ac filters or furnace filters restricting the air flow in older systems?

If you have been using a pleated filter for a long time, 2-8 years plus, with no problem, then you are keeping your coil clean so stay with a pleated filter with the same Merv rating. If you have a metal or plastic electrostatic filter that you are washing, then you should change it to a pleated filter. You can never get the electrostatic filter clean enough and they restrict your air flow when they get dirty which will cause your electric bill to increase.