Hmm........ in melee combat, LegendaryGoji has this in the bag. However, as far as we know, Heisei has the edge in his special powers. Soooo........ depends on the range of combat, and who can strike the other the fastest.
Heisei Godzilla has it. Legendary might have the advantage in close combat, but Heisei Godzilla has nuclear pulse and the Red Spiral Ray. There's just no way Legendary's Godzilla could counter that.
As above, but the 1994 godzilla heisei is more powerful then 1984, who is heisei but would lose.
Keep in mind......................................... we only EVER saw Godzilla 2014 use his atomic breath on the female MUTO. We don't know how destructive it is because he never used it on buildings or anything. And just as Godzilla evolved the atomic breath as a natural weapon against the MUTOs, the MUTOs probably evolved at least SOME resistance to the atomic breath that made it so they could never get burned from the outside.
Also, Godzilla 90's is painfully slow and has trouble in close combat while Godzilla 2014 is actually pretty agile for a Godzilla. Given that Godzilla 2014 can take nukes to the face and survive with no harm at all, I am quite sure that he can survive Godzilla 90's's atomic breath, then brawl with 90's and eventually overpowering him.