For me its Goliath, Behemoth, Wraith, Kraken.
I put Goliath at the top because many Hunter tools like Mines and Harpoons seem built around him and are the most fun against him.
Behemoth tends to vary greatly with player skill in my experience, particularly with how they use Tongue Grab and Rock Wall.
Wraith can be an annoying coward, but nothing is less fun to fight for me than Kraken.
His mobility makes him practically immune to the heavy-hitting Assault tools, CC does next to nothing against him, and he can deny revives from the far end of a Dome with ranged attacks.
In my experience playing against Kraken is a game of constantly shooting long-ranged weaponry and hoping he can’t aim Aftershock or Lightning Strike well, both of which can take two dodges to avoid.
If the Kraken knows how to land his abilities and doesn’t mess up, the Hunters are basically screwed.