I chose Gvs.MG‘93.
With the exception of GVS.M '92 and Gvs.SG, the three remaining choices strive for having a dramatic story. In terms of Gvs.KG, the time-spanning story does good, when it comes to aspects like Shindo and aspects like him who are part of "the past". The emotional heart is there, for that Shindo's death scene really is going for that tear jerker quality. But then you have some failures, such as the love triangle and the social-economical side of the story. There is some nice commentary in relation to Japan's Tiger Economy years, but nothing too impacting - particularly with the story. A lacking of the fleshing out of the love triangle is what hurts most, with the government side of things being handled the way it probably should be (professionally).
Gvs.D works the usual "final film" attributes by relating itself to the first film of the continuity. When I was younger, I might have felt something for whenever Ken Yamane would detail an Armageddon scenario followed by a CG-fueled demonstration. I don't now. The film is just a bit of ineffective filmmaking on the human side of things. One of the best things about the film - Momoko Kochi - is underused. As if the filmmakers thought the audience would rather have more of a descendant of Yamane's we just met rather than the genuine article who we knew from the original film. More than that, all of the family relationships in the film really don't matter unless it's a kaiju family relationship. Sure, Ken had to ask Yukari to have the good doctor keep on exploring micro oxygen as to possibly make a weapon against Godzilla. But of course we know Yukari is going to say yes. Ken's family and the good doctor is a love interest. That's just predictable. When it comes to the kaiju relationships, there is some effective drama. Junior dying was a great moment. Godzilla's meltdown was another great moment. Destroyer being a bad guy when he owes Godzilla for his existance is also a nice touch (and makes it even more sad that Junior had to die at Dessy's big obese hands). Kawakita wasn’t much in way of pioneering special effects, but he shows that he does have a flair for emotion and grandiose in his directing when he is at the top of his game.
But now, the one I chose, Gvs.MG‘93, truly is one of the best. A good part of the reason why it works is precisely the kaiju relationships. Godzilla and Rodan fight over baby, and even in light of a common enemy (Mechagodzilla), neither really team up or stop fighting each other until death is a 100% guaranteed occurrence (especially in case of Rodan, who finally had to balls to help Godzilla out in death). Of course, Mechagodzilla is not emotionally involved with the fight, but in return is a device that helps the humans inject themselves into the kaiju drama. The need to get rid of Godzilla, along with the general lack of care for Baby by pretty much everyone except for a couple of key people, all of that plays big parts in how the story could twist ands turn. Where the film fails at is only when it gets down to Kazuma and Azusa and the utter lack of drama between them. If she knew about it, she would have been upset with Kazuma's wanting to get Garuda to be an accessory for MG along with possibly fleshing out Kazuma's moral being. But that is missing from this potential love interest angle.
In the end, all of the films suck as far as the development of possible dramatic elements of the human elements, thus it comes down to the kaiju relationships and how well they are tied into the human relationships. For those reasons, I pick Godzilla vs. Mechagodzilla '93.
Extra points to Gvs.MG ‘93 for not only having a great theme for MG, but also bringing back a piano theme from Gvs.KG which sounds completely ruthless when used in a kaiju battle.