The hippo for sure. A giant lobster would be pretty scary, but I imagine a Hippo could easily crush it. With its sheer weight, or even its jaws. Hippos ain't no fuckin' joke. There's a reason no one fucks with them, and when someone does they get rekt. Also, I don't know much about lobsters despite being originally from New England, but I imagine they're kind of like crabs in that their limbs can get pulled off very easily. So yeah, hippo wins.