It's just a $10 difference so it's up to you if you prefer 2GB or want to save a bit of money with 1GB. Having twice the VRAM means it could last longer, yet from the few reviews I've found, it doesn't make a difference in framerate, and for recent games you would probably be playing on reduced settings anyway.
eTeknix reviewed the Sapphire R7 260X 1GB and it more or less tied with the reference R7 260X 2GB in framerate in every game they tested.
You didn't mention an overall budget and you were asking for ways to actually cut down on the price, so I was more concerned with keeping it as low as possible, despite the my recommendations already costing more than your build. I felt that moving up to an i3 processor justified the higher cost, but the 2GB model didn't.
Well, I guess it boils down to when you intend to upgrade the computer after building it. The 2GB model will last longer but it won't change framerate performance or anything, just how high you can crank up textures.