The way I see it; it’s not a Goliath since they can be easily captured and contained.
It’s not Kraken because he’s hard as hell to bring down and I can’t imagine that he would have the capability of surviving in space.
It’s not Wraith because if more brute force Monsters such as Goliath can’t even break out then how am I expected to believe she can destroy a ship let alone escape a relatively small container on Wraith Trap.
It’s not Behemoth because despite him having the power to conquer worlds Torvald specifically states that we would “Know it when we saw it”
And it’s not Gorgon for the same reasons and also I can’t see her living in space.
I may be wrong on all of these but it’s how I see it; as far as I know I think how @Matthew’s ideal solution is how it should be, one day a new Monster will be made and an adaptation of that Monster will be the one to have destroyed the Ajax.
P.S There’s no interesting lines with Torvald for winning against the Queen. At least none that I’ve encountered.