Just to compare the new Vitz to a more known car and which most people tell not to get the 1.0L, the March K11
http://specs.cars-directory.net/~compare?ids=MzYzNDQsMTg5NDksMTg5OTksMzYzNTA=
If you check the K11, assuming the fuel and passenger weight to be same, the K11 has a better power/weight ratio than the Vitz in both 1.0 and 1.3 engines. The fuel consumption is excessive for the K11, yes, but power wise, for a family, shows the 1.3L to be better as it's too much load on the engine when 1500kg+, especially for the 3 cylinder 1KR-FE. If you travel alone on flat land, the 1L Vitz should be the most economical, even stats show that.