Part 7 is definitely the most well-rounded. Johnny's easily the best Jojo (I can entertain a debate of Johnny vs. Joseph but nobody else even comes close), Funny Valentine sits with Kira as the best Jojo villains, and Gyro is definitely on the high end of the companion tier list.
I've actually always really liked Part 6 despite it having a lot of dumb shit in it. The plot was nonsensical, the side villains and their stands were mostly really dumb (especially egregious after Part 5's excellent villain cast) and Pucci himself is like a C-tier big bad at best, but Jolyne, Foo Fighters and Weather Report kinda carried the part for me. I especially liked Stone Free, which was refreshing after the utter bullshit that was Gold Experience. During the fight with C-moon I totally saw the whole mobius strip thing coming from a mile away and I loved it, because I'm so used to Jojo fights being resolved with asspulls.
I've always seen Part 5 as Part 3 but better executed. They're both road trips with a large main cast where the gang fights two different groups of enemy stand users working for an evil guy with time-related powers, with a good chunk of the tension coming from the team trying to figure out how exactly said evil guy's stand works, ending with the Jojo gaining a powerup that directly counters said time-related stand ability. Oh, and they also have super bland protagonists, except I actually like Jotaro because he's just a massive autist while Giorno was just super bland and personalityless to me.