Furious 6 was overall my favorite one (where they go to London to help The Rock, in exchange for pardons and getting to go home to Los Angeles), because it had the biggest cast of characters of all the movies andthe most amount of character stories. xD It was like each new movie got bigger in bigger in terms of people in the "F&F family" AND the scale/technical execution of its action, and Furious 6 was the culmination of all that. :) It then went downhill with Part 7. :( They should have stopped at 6 in my opinion lol, since they were all free and back home in LA at that point, and it already explained why Sung Kang decided to go to Tokyo (to honor Gal Gadot's last wish). They should have left it at that, overlooking the LA skyline while Tyrese said grace and made a toast to fast cars. It was a perfect ending. xD
I also really liked Part 4, because it was the first time in like 8 years that we got to see all the original characters back together again, and it had the most drama because of that. xD PLUS, it had my favorite car race in the whole series: the nighttime LA road race between Vin Diesel's Chevelle and Paul Walker's awesome blue Skyline. :D
All of them were good, except towards the end it kinda turned more into action-gratification but I loved them still. My favorites were 1 and 3 though. 3 cuz I love ricerunners lol and 1 cuz... it's the original.