HRA is less a movie about a car than a movie in which one of the characters happens to be a car. That said, it's the second best in my opinion. No racing, which is lame, but the writing and humor are still as smart as they were in The Love Bug, if not more so.
HGTMC has some of the best racing scenes and Herbie looks the coolest he does in any of the movies, which earns that movie points. Plus it has the return of Dean Jones and the inevitable car love interest for Herbie. And Don Knotts, who is one of those actors who can do no wrong no matter how dumb the material. But the jewel heist plot is contrived as can be, the car romance is handled in a painfully cheesy manner, as someone else says, many scenes drag on much too long, and a lot of the jokes feel a bit dopey. Plus Jim Douglas has mellowed, which makes sense given his character arc in TLB, but in this he's mellowed to the point of being a pushover. He turns the other cheek to the point that you just want to shake him--luckily he has Herbie to stick up for him. In TLB he didn't take crap from anyone, which made him too arrogant (and in need of a humbling lesson) but surely there's a happier medium than this. (Incidentally, the TV series further accentuated Jim's slide into being a hapless patsy for whoever wanted to push him around. Aside from the general uneventfulness of the show, this was the worst thing about it.)
In Bananas, director Vincent McEveety, who also did MC and would go on to helm the show, took the dopiness even further, incorporating a little "na-na-na-na-na-na" singsong jingle into the theme song (something else that would get worse on the TV show). Bananas is worth watching because it has some of the best, most convincing car stunts and the best wheelie of any of the films, and that's about it. And Paco is fun to watch when you're a kid and wish you could drive Herbie, even though when you get older you realize he's tremendously irritating. Lots of the jokes are just plain dumb, and comic talents Harvey Korman and Cloris Leachman are left to flounder.
That part about Bananas is irrelevant, because I mainly wanted to respond to the HRA vs. MC comparison, but I built up the momentum and couldn't stop.