I have loved every Fallout game that I've played. So settings/plots/age of the game don't really change my opinion on them. But since Fallout 4 has run phenomenally for me (on PS4) and has added features like the base building and a hot keyed grenade button/just overall better combat. It has my vote.
Let's face it; Fallout 4 was an IMMENSE disappointment. New Vegas has more to offer on literally every conceivable level, except graphics.. I will also admit that the Fallout 4 map is a lot more fun to explore.
However, New Vegas has a wider variety of weapons, better character development, better replay value (fo4 has virtually none), more factions, more meaningful decision making, decisions that ACTUALLY EFFECT THE WORLD, dialogue choices THAT ACTUALLY MATTER, etc etc.
Its similar to the morrowind/oblivion or oblivion/skyrim situation... Significant degradation of all gameplay mechanics for the sake of better graphics... Not a good recipe in my opinion.
Its just like all of the fallout games and it really fun don't you think so so what its like getting a toy it gets boring after a while don't you think and what are you going to do when it gets scratched because on the inter net you half to get a shipping fee