Answer:
I would rather encounter Cyclops instead of Scylla.
Though a Cyclops is a monster, he's one eyed whereas Scylla is a sea-monster with six heads. And sailing would be a hazardous effort with her being in the water.
Step-by-step explanation:
Cyclops is a one-eyed creature, the son of Poseidon. And even though he's a descendent of the sea god, Cyclops mostly reside on land and are similar to humans, domesticating and living in one place.
On the other hand, Scylla is a sea monster with six heads. This will make sea journeys a disaster, for she will rule the seas.
Sailing requires a journey on the seas, which is the realm of Scylla. It is her home-ground, where she knows everything and is capable of destroying everything. A Cyclops may be dangerous but not that hazardous for sea travels.
So, I would prefer to encounter Cyclops rather than a sea monster.