That's a really tough one, there's a lot of good ones.
Most fish I guess, can't go wrong with a big hungry fish. Also anything with a long neck, so quite a few dinosaurs and birds. Frogs and toads are another great one. And then there's slugs, those are amazing. Oddly, most bugs and spiders are also really cool in vore, at least when swallowing whole. Also worms.
I can't really decide, there's so many good ones