The most common car comparison is
comparing two cars built on the same platform. For example VW build about twelve different models on the VW Golf platform. There are ten different cars built on the Ford Focus platform. I imagine searchers are looking to see if there's an advantage in one or the other.

However if cars are the same size and rank closely for performance, emissions and fuel consumption there's little difference. You have to remember figures for fuel consumption are produced in a laboratory. If they rank closely there may be no difference in real on the road driving.
Typical comparisons are:


Ford Fiesta vs Mazda2
Skoda Fabia vs VW Polo
Skoda Yeti vs VW Tiguan

The above are cars in the same class. It can be different types of car are built on the same platform. For example the Nissan Qashqai Crossover SUV and Renault Scenic MPV are built on a Megane platform as is if I remember correctly the Clio - four types of car on one platform.

There can only be three differences if cars are the same class and size with the same efficiency figures. Two are style and comfort which are both subject to your personal taste.

The third difference is price. If a seller can make a service or product appear different and sell it through a different outlet and promote it in a different way then they can charge a different price. So it's up to you if you wish to pay the difference.

Regards
Ralph