I really like Ferrari's slogan in the game because it's a quote directly from Enzo Ferrari, the founder. It's also my favourite brand so who would have guessed? I like the slogan by itself too, the constant progression of their cars and technology. There is no best car because it's constantly getting better.
Now time to roast some rival manufacturer's slogans, it's time for some zingers:
Bugatti: "Art Forme Technique"- Styled by world-renounced arthouse Jelly Belly.
KTM: "READY TO RACE" - Doesn't even have a car eligible for any of the Gr. classes.
Daihatsu: "Light You Up" - ...and proceed to take my phone and wallet off my bullet-ridden corpse.
Zagato: "Collectibles Since 1919" - Too bad your car's fake, so you'll never be able to collect it anyways.
Dodge: "Domestic, Not Domesticated" - Your cars handle like domesticated farm animals too.
Honda: "The Power of Dreams" - Dreamt up four variants of the same car. Pretty unoriginal.
Ford: "Go Further" - Challenge accepted. I can easily go further than those lampposts that your Mustangs crash into.
Citroen: "Inspired By You" - Unfortunate that everyone who drives a Citroen is a simpleton.
Audi (Translated): "Truth in Engineering" - The truth that I found in your engineering is that your cars suck. Got 'em.
Lexus: "EXPERIENCE AMAZING" - Experience two bloated, heavy GT cars with controversial styling.
Aston Martin: "We make beautiful art that is meant to be driven and enjoyed" - I wouldn't call that pig the DB11 (coming soon™) "art".