Ignoring the Showa Era series of Godzilla who can pretty much make up powers like flight and magnetism randomly, I still say Heisei Era and up of Godzilla still have the advantage either way.
1. Surviving a nuclear explosion but still being heavily injured by it just shows how Slattern's durability isn't actually as good as Godzilla's. In Godzilla vs King Ghidorah, the same thing happened to Godzilla underwater and yet all it did was make him stronger and larger. Hell, Heisei era Godzilla tanked a volcanic eruption while inside said Volcano and emerged unharmed. Volcanic eruptions can approach or even surpass nuclear explosions. Or surviving a meteor impact that level an entire area of a city leaving no
2. Farther reach in comparison to what exactly? Ranged attacks make it a moot point.
3. You're going to have to provide feats of how strong that electrical attack is considering Godzilla's atomic rays have concussive force to blast other monsters massive amount of distances and explosions that rival nuclear weapons even before the upgraded spiral ray.
4. Slattern is agile, fast, and intelligent? So are many of Godzilla's opponents and they've actually shown sentience. Many of the flying monsters like Rodan or Kamacuras have shown supersonic movement after all. The idea that Slattern is bigger is false. While Slattern is indeed more voluminous, even the smallest version of Godzilla weighs in at 20,000 metric tons while Slattern is at 6,750 tons (and the rest of the Pacific Rim cast at far less than even that). They essentially would be classified as featherweight; big, but effectively made of styrofoam. The fact that Heisei Era and up Godzilla can lift things nearly double his weight like King Ghidorah at 70 000 tons and fling him away just shows the difference in physical capabilities.
Based on actual feats, there isn't much that Slattern has done that hasn't been replicated or surpassed by other monsters in the Godzilla series.
Godzilla allied rarely starting with the Heisei period. Though, Rodan's sacrifice when Godzilla actually first got killed by Super Mechagodzilla pretty much upgraded him with the Spiral Ray that was used to pretty much stomp every other monster in future movies.
Jaeger's use blunt force and energy weapons will be pretty much useless against Godzilla. I'd say Crimson Typhoon has the best chance with its rotating saw blades, but I doubt they'd be as effective as Gigan's gigantic buzzsaw on its belly. It'll have to attack Godzilla over and over again before its regeneration could kick in with the disadvantage that one solid blow from Godzilla might end it.