1, 2 & 6 are Definitely the best movies in the series. But as far as entertainment goes, 3 and 4 are pure awesomeness
And every rocky fan knows that there is no such thing as Rocky V.
I love the whole franchise, don't get me wrong, I grew up on 3 and 4 and didn't like the original 2 until adulthood, they lack entertainment for a kid, you really need to be older to appreciate the story, 3 and 4 have more fighting and things a kid can get excited about. For me the American flag shorts will always be Rocky to me, even though that's not his colors but Apollo's, that's how I knew him for so much of my life.
1,2 and 6 just have a flowing story arc for Rocky, 3 and 4 are more like adventures along the way, but if the franchise were only 1, 2 and 6, the story arc would work. The stories of 3-5 don't contribute to where Rocky is in 6, he's not in the house from 5, you don't have to have why he went poor in 5 because the end of 2 has him win, doesn't make him rich.
Rocky 5 would probably sit better if it hadn't been the last film for so long, if it were just a stepping stone all along, it might have been different, but it was made to be a finale and it sucked as that. It has flaws period, but a lot of the issues stand out because it's like, this can't be the last look at Rocky we ever have, they overdid the brain damage and all. For whatever went wrong with Rocky V, the scene of him in the gym reflecting on Mickey training him for the Apollo fight was one of the best scenes in the franchise.
For me, 3 things make the Rocky series really work great, Stallone, Bill Conti's music, and Burgess Meredith. As fun as Apollo is, killing off Mickey hurt a bit, and no Bill Conti music hurts 4 a bit, and those 2 were the only thing that kept 5 afloat. Don't get me wrong, you need Apollo and Duke and Adrian and Paulie, but those 3 really define it for me.