What I stated is exactly true. There was no standardized criteria. The FACT that the responses were sorted by political affiliation even goes further to show it was opinion based.
If I wanted to ask mechanical engineers about the best engine, I'd expect them to rank them on various component performance and the presence or absence of various things making the engine work. For example, they might rate them on horsepower to weight, horsepower to volume, complexity, or other measurable qualities. The same could be done of presidents.
You could use things like, treaties enacted (not just started but ratified by Congress), or how much did they add to the national debt? Maybe, polling numbers (538 makes that easy for modern presidents). Handling of crises. Major legislation enacted. National economic performance while in office. There's lots of measurable criteria that can be used here. But, for the survey in question, none of that was used as each participant was allowed to choose their own criteria.
