In an actual comic Doctor Octopus would win this encounter more likely than not.
Because he would have enough sense to come equipped with some means of dehydrating Namor and robbing him of his strength.
Namor would win most random encounters against a normal unprepared Ock, though.
Namor would win a majority of engagements, though not all, against normal unprepared Adamantium-armed Ock. That version took down Hulk and has to be given consideration because of that.
However, Hulk cannot fly, and Namor can, and would thus have options Banner didn't.
Namor, again, for the majority of forum battles, though.