who would be the villain?? There's been a handful of wannable Atlantean conquerors (Attuma, Byyrah, Krang, U-Man, etc.), and then there's guys like Tiger Shark. Who'd be worthy of being Namor's movie nemesis? 
 
My choice would either be Krang or maybe Tiger Shark. With maybe an appearance by the giant whale kaiju Giganto. :P

It depends on what kind of Namor movie they do.  If they go for a less superhero movie in the vein of John Byrne's run, they could use big business, especially the oil companies.  If they go for a fantasy movie, they could use Suma Ket.  If they go for a period WWII piece, it would have to be U-Man.  If they would make some epic mini-series like Dune with Atlantean intrigue and politics, I'd say Byrrah and Krang.  For something SF or a cautionary tale, I'd use Tiger Shark.  Though, he could do well in just a general superhero too.
 
But the one I really would like to see is Llyra.

Attuma and Tiger Shark.

Attuma, teamed up with the oil companies. 

I'd be happy just watching him sink u-boats. 

The perfect adversary for Namor would be THE Human Torch. I think that would be awesome build up to a WW2 Invaders movie.

I could definitely go for a period movie with Namor sinking U-Boats. :)
 
Human Torch is a possibility I hadn't considered, but I'm not sure they could do two origin stories in Namor's movie.

I agree on Attuma, would make an awesome villian in a Namor movie.