GODZILLA: The Best and Worst Adversary (Showa Series)

As an avid King Ghidorah fan, especially the Showa version, I can hardly argue against the three headed king of terror. Although one could make an argument that perhaps Hedorah or MechaGodzilla were tougher, I don't think either had the same amount of charm and insanity as the unhinged King Ghidorah. (Although he was looking worse for wear in Godzilla vs. Gigan and Zone Fighter.)

Otherwise I'd say Kamakaris is the least memorable, though I have massive respect for the critter these days due to the incredible puppetry and wirework.

Strongest is probably Ghidorah, with Mechagodzilla being a close second

Weakest is a toss up between Kamakaris, and the Giant Condor, but I hate the Condor so I'll give it to that.

King Ghidorah, definitely. He always gave Godzilla a run for his money. He had personality and when you heard he was on his way, you knew a good fight was about to go down. In my opinion, it's a tie for a close second of Mechagodzilla and Gigan, both of whom tormented Godzilla on more than one occasion and always made him work to win. Hedorah also was surprisingly resilient and challenging for Godzilla to defeat, so he definitely deserves the recognition too. (also, design-wise, I think all of the above foes were significantly above average) 

Weakest in both design and power would be Giant Condor, Gabara, and Ebirah, in order by how bad I think they are (I like Ebirah better than Gabara, while the only reason Gabara is in front of Giant Condor is at least he has a name and more than 15 seconds of screen time) 

My pick for toughest would be Hedorah. He was getting bigger and bigger and if it weren't for the electrodes, i have my doubts as to whether Godzilla would have got the best of him. Worst I'd have to say Gabara. He was just too easy and he even had a hard time against Minilla. Just mho

For me the best enemy is MechaGodzilla. Not only did it take the combined efforts of both Godzilla and King Caesar to finally stop him, but He is also one of the only monsters to cause Godzilla to bleed.

The worst enemy on the other hand would have to be the Giant Condor.