Spark Plugs for 73 Dart Custom

Hey guys I'm looking into getting new spark plugs soon and have been wondering if I should try something different. It's a 318 and I've only ever used Denso Iridium plugs in it before, they also foul very quick. (Engine burns a good bit of oil) Is there a difference besides price in going down from iridium to copper plugs? What do you recommend or buy for your old cars?