New Vegas is my choice, more dynamic story is more important to me than the dynamic world of Fallout 3. If Fallout 4 can do both in quality and quantity, well then, I'd suspect that BGS and Obsidian worked together.
From reading peoples posts, compiling the opinions and adding my own.. this seems to be the best course of action. Its like a super team. Thinking about it, they would be MAD not to combine their efforts!