In terms of environment / story, I liked Fallout 3. Maybe it's because it was the first time I played a game like that, but I liked the open world adventure of just taking off in a direction and finding something.I like Fallout 4 and New Vegas equally, but for different reasons.
New Vegas had the better stories and setting, but I do enjoy Fallout 4's gameplay and settlement building.
I do wish that Fallout 4 had NV's faction reputation system.
New Vegas was clearly the better RPG. The complex story lines and interactions between various people and factions. I mean some of the stuff going on in the casinos you’d need a guide to figure out.
The thing I disliked about New Vegas was the lack of random encounters / combat. You could walk from one end of the map to the other without finding a single person to fight.
Fallout 4’s world was beautiful, the game play mechanics were great, but really nothing you did had any real impact on the world.