I want to get all of the free cars. I know that some cars are platform exclusives - for example Samus Gunship for Switch.
What are the exclusive Xbox cars?
According to the Rocket League Wikia:
The PlayStation 4, Xbox One and Nintendo Switch versions also include console-exclusive unlockable Battle-Cars (Sweet Tooth for the PlayStation 4 version; Hogsticker and Armadillo for the Xbox One version; Mario NSR, Luigi NSR and Samus' Gunship for the Nintendo Switch Version). Bodies record the number of matches won while equipped.