Car Selection
For a game that shares so much of its DNA with the classic GTA free-roamers, car selection is surprisingly unimportant in Mafia:3
In the early phase of the game, the best car to steal is whichever car is closest. It's better to grab a moderately fast car and be on your way than to jog two blocks scouting around for something that might get you there ten seconds faster. There is also an element of common sense – if speed is your aim, maybe don't jack a dairy van.
In the second phase of the game, when you can have a car delivered to you at any time, take your pick of that limited selection. Again, there may be faster or flashier cars in the game (the DeLeo Capulet, for example), but you can't save them, and it's not worth the trouble to hunt them down.
Later DLC promises to alter this, but for now the best car in New Bordeaux is the one you can get your hands on fastest.
The image featured at the top of this post is ©Square Enix.