Fallout

New Vegas and 2 are the obvious choices, but I'm going to go out on a limb and say that 76 is third. Speaking as someone who didn't enjoy 3 and 4, 76 fixes a lot of my gripes with those two games while simultaneously having some of the most creative world building in the series. The game taking place shortly after the bombs dropped makes Bethesda's heavy focus on pre war America fit a lot nicer than everyone constantly talking about a war that happened 2 centuries ago in 3 and 4. The various factions, from the Responders to Foundation to the Cult of the Mothman, are creative and have a lot more depth than any faction or settlement in 3 or 4, and feel a lot more interconnected in the world. Appalachia is also just really awesome to explore