Samishe does have it right. It does take a Thunderclap for Hulk to hurt a symbiote. He learned that one the hard way. However, stop the fighting! Batman would get eaten by the Hulk, so I don't think that's gonna work. He doesn't really have a chance against someone that big, or strong. Also, Hulk nowadays still has the intelligence of a normal man, since he's another personality. As for the classes, here's how I've seen it.
Venom's a class 35 at best. Maybe 40, but nowhere past that. Carnage is about 40 at best, but can soak up sonics better, and is a bit more durable. The blades and weapons he can create from his symbiote are nearly limitless, since he's psychotic. Now, Toxin is the most powerful of the symbiotes, and only his uncle Hybrid is right below him. He's a class 75, and still growing. His claws are one of his main weapons, and he's fought villains of Thor before. (I loved it when he picked up the crowbar!) Now, although this would be a tough fight for Hulk, considering these three would be bouncing around like crazy, considering they're as quick as Spider-Man before The Other. However, The Hulk would win this one, because although we're trying to limit him without the Thunderclap, for him it's a reflex. I'm a huge symbiote fan, but Hulk takes this one.