The 54' film is a masterpiece, but there's a lot of limitation in thought to consider it a bar which can never be touched. Hell, I like Monster Zero more than 54' (SHARPEN YER PITCHFORKS LADS) because of the fun characters and a more polished production that comes 6 films in.

King Kong vs. Godzilla is, of course, a comedy. Mothra vs. Godzilla is a return to a more traditional scifi adventure narrative ala Raids Again albeit much more effective. I consider these both very highly. They are distinct and still memorable entries in the same franchise.

Ghidrah, the Three Headed Monster is literally an Atom-Age fairy tale. A princess in danger? A Dragon? A Knight? Monsters that speak? Throw in some Roman Holiday and you've got something that fits alongside Kong and Mothra vs. but offers viewers a different vantage.

Then you have a straight up Alien Invasion/Buddy Film that while including LIZARD GO JUMP is probably the most straightforward handling of the Nuclear Weapon analogy since the 54 film. (They negotiate the miracle drug for weapons that they in turn immediately abuse.)