Note that, unless the island is really big there simply won't be a huge number of large predators. Big predators require big home ranges. An 6000 kg adult T-rex (mid-range of estimates), probably required a home range of many thousands of square kilometers. Even an island with a 20,000 sq km area (that's a big island, slightly larger than New Caledonia) is pushing it in order to maintain enough apex predators to sustain a viable population. Unless the party explores exhaustively they'd be unlikely to encounter more than one individual.

In terms of big, nasty predators likely to threaten the party you probably want to focus on something no more than around 500 kg - slightly under twice he size of a large tiger. Something like Ceratosaurus fits the bill. They would be much more common. Even smaller dinos, perhaps around 100 kg (this is the approximate weight of a lioness), could plausibly operate as pack hunters.