Is it really settling it to ask DA? Regardless I thought 3 was really the best. New Vegas was really interesting and well-written, but the landscapes got a bit boring as I felt like I was tromping through regular Nevada for half of it. 4... between lazy writing, lack of content, and the focus on the needless base-building mechanics, hands down the worst in the 3D series.
Gameplay in my opinion goes to Fallout 4 due to settlement building and modifications of armor, weapons, etc. And the game mechanics regarding the Power Armor (you don't need to remove you any armor or garments just to wear Power Armor parts).
Story-wise, location and setting, my vote goes to NV, even though i have only played the vanilla version.
While 4 was BIG, it just didn't have the character of NV. I cared next to nothing about helping any of the factions in 4. Beyond the base game, the DLC for 4 fell way short of the bar they had set with 3 and NV. 76 has me curious, but I'm not sold just yet.