On a boat no land for a billion miles...
I wanna say Mera but I know more often then not Arthur would Win. But Mera seemed to be specifically trained for that purpose. I will have to give it to Aquaman. The better weapon and his strength should counter what ever skill set she has as far as melee goes.
Aquaman I believe has the advantage.
a) He can use his telepathy directly on Mera
b) He can use his telepathy to summon stuff to distract her (like Krakens, sharks etc)
c) He is established as far superior physically to all other normal Atlanteans (like Mera)
d) He has the Trident
e) He has more experience than Mera (Mera 4 years ago was still training, Aquaman 6 years ago was already leading his own team, the Others).
@guardiandevil83: She is an Atlantean, from the rebel Atlantean colony of Xebel. Her father indeed hated Atlantis because for some unknown reason (so far) they were banished there.
Aquaman is the only super Atlantean (confirmed through feats and most recently directly in Aquaman #21). This is in accordance with pre Nu52 continuity.