That's the thing, the GM is not sure in what part he wants to place us... last I heard he seemed inclined to place us somewhere in or around the Riverlands. I have to admit, I know very little about that region so if he does pick it I will feel a bit lost! Hmmm, I guess my house name should reflect my heraldry or vice versa. I would so love to sneak in something that is DA related, but griffons are way to obvious and doesn't really seem to fit the style of the Riverlands. Any suggestions?
Hmmm, I wonder if I can sneak an egg in there somewhere... 
It shouldn't matter where the campaign is set as long as you have good reasoning for your character to be there. Like you could be from Dorne where you serve a family which made its fortune on the spice trade, and you were originally sent to the river lands as a trade emissary/distributor.
But if you really want to be from the river lands I would suggest the dalish heraldry with the bow and arrow (a house which was founded on its excellent hunting and archery skills ). Another option could be the circle symbol which you can give new meaning.
Oh and I would steer clear of mabari because of house clegane.