Whichever one earns more dollars is more productive in terms of dollars. If you want to do this right, pick a good metric (plumber dollars is fine), then optimi

Whichever one earns more dollars is more productive in terms of dollars. If you want to do this right, pick a good metric (plumber dollars is fine), then optimize your workforce for that metric. Do not reward them for that metric or it will be gamed. Consider other metrics that are important (e.g. customer satisfaction) and set constraints on the processes that set a standard that must be met. Not objective, not right 100% of the time, but let's not pretend its impossible to improve processes with some sort of goal in mind.