On land I'd give a slight edge to Namor most of the times due to his flight, though AQ can pull some wins due to speed, telepathy and he can leap to reach Namor.
Near water or underwater Aquaman would win due to his telepathy (both directed at Namor or by summoning creatures to keep Namor occupied and deal some damage) and greater speed.
Originally posted by Golgo13
Aquaman if he's allowed telepathy and or Water Hand. It would be spite, IMO. In a hth battle, Namor, but DCnU Aquaman can probably split even.
The op specifies no weapons but doesn't say anything about powers.
Even without telepathy, AQ should win underwater due to speed.
Namor still has the flight advantage on land.