What is the most popular car today?

Prius

But that is quite an expensive car, though it can run on petrol or the electricity stored in its batteries.

A more likely candidate is a Ford, particularly the Fiesta.

If sales is an indication of popularity, which it for sure is, then the Toyota Camry is the most popular car in the U.S. as it sells more than anyone else and has since 2002. The Toyota Prius, as mentioned above, does not even rate in the top 10 but is the best selling Hybrid. The Honda Accord is the most popular as of April 2013 and is outselling the Toyota Camry but the year is not over. The most popular car in the entire world is the Toyota Corolla which outsells every other model.