As of my last knowledge update in October 2023, electric vehicles (EVs) generally offer the highest efficiency when compared to traditional internal combustion engine vehicles. One of the most efficient electric cars is the Mercedes-Benz EQS, which has an energy consumption rating as low as around 15.0 kWh per 100 miles. Another highly efficient model is the Tesla Model 3, particularly the standard range versions, which also showcase impressive efficiency ratings.
However, efficiency can vary based on factors such as driving conditions, load, and the specific configurations of a car. In terms of overall efficiency ratings, it's essential to check the latest EPA ratings or equivalent evaluations for the most up-to-date information. Additionally, new car models continuously enter the market, so new contenders for the most efficient vehicle could emerge.