There can be only one,
A manual BMW 3 series with a 1.9 liter gasoline chain driven engine (as opposed to belt driven).
But now that I look at the market in Cali and the rest of the US there's really only offers with massive engine blocks starting at 2.4 liters. Are you all race car drivers or something? Really what is it with enormous things in the US...
The BMW 318i that I mentioned does close to 30MPG.
BMW has been making engines since the beginning of time, as such their engines are the most efficient you can find on the market, especially on the US market. The cabin is engineered to insulate you from unpleasant outside noises, the engine has a nice low gentle lion roar to it if you put your foot down. There really is no such thing as better when it comes to BMW, it's a work of art. Even closing the doors feels like it tries to show off it's subtlety and precision engineering.
Cars to look for; BMW, Mercedes, Volvo, Audi, Renault, Tesla.
Cars to avoid; Peugeot, Citroen, Kia, Nissan, Skoda, VW, and obviously anything American made like Ford.