For me, it private land or nothing. That's up here in the northwest corner of the state though.  

I grew up in Los Lunas. I cut my teeth duck hunting on the Rio Grande. Back then the ditches weren't locked and you could go anywhere.
I think you can get a key to the ditch gates from the conservancy district in your area. Once you do this, you will have access to the entire river.
I would imagine the south end of Bernalillo county would be pretty good.

Don't be afraid to ask people if you can hunt.  Ducks are not like deer or elk. Most people don't care about them. A lot of farmers want to keep geese off of their land, so they will encourage hunting. I know one older man that calls me when the geese are coming into his fields. He gets bugged if I don't go. Hunters are like free pest control.