Let me post an example of relative merits between these three fuel efficient technologies:
- Insight - great mileage but lean burn was not the lowest
- Prius - good mileage and car had very low emissions
- Diesel - OK mileage and emissions issues
Some of us don't really worry that much about who has the cleanest tail pipe. If there had been a five seat Insight with adequate size, it would have been a serious contender. But when I bought my Prius, "lean burn" had pretty well disappeared and the Insight had too little space for our family.
If I can figure out how to give my NHW11 Prius a "lean burn" capability at cruise speed, I will. This could significantly improve my cross-country mileage while dumping the NO(x) fertilizer gas in the bordering fields. But this is not a trivial technical challenge.
As for diesel, the mileage doesn't make sense in what is available and the past diesels earned a poor reputation. But "lean burn" and diesel thermodynamic cycles are pretty close to each other.
Bob Wilson