My favorite one is and always will be Tokyo Drift. I know it isn't very popular among the F&F fans, but I like the campiness aspect of it, and most of all, I like that the center of attention is actually about racing and not about heists. To me, that movie has all the elements I need to enjoy a movie, and there are no boring parts, and I appreciate it for being probably one of the last "90s type" movies that will ever get made. Which of the Fast & Furious movies do you like the best?
My favorite is Fast Five. It had lots of insane stunts and cool looking cars which kept my adrenaline pumping all throughout the movie. The action sequences are great too and the addition of Dwayne "The Rock" Johnson to the series was a great move. The Rock and Vin Diesel have such a strong presence when they are on screen.
I'd go for part 1. It all started there. The story is great unlike the other parts are a total exaggeration especially the last 2 ones with the Rock on it. Its not just unbelievable but they have made it unappealing to some Fast and the Furious fanatics. Involve drag racers and thieves to an all out war battlefield, possibly not, but if its a World War it might possibly.
They incorporated gang wars and fire fights and thieves because a movie sequel that's purely about drag racing could get old real fast. Just imagine if the the first until the 6th movie was purely about drag racing and stuff like that. It would be very monotonous and would only appeal to a small audience - those who love racing.