If for fallout 3 blackout enb is pretty good or fallout 3 midhrastic enb although blackout was designed with fallout new vegas in mind you can adjust a few things to get it work properly if you need help with it just let me know!
For new vegas Dynamo, Blackout, and rudy. Dynamo and blackout are much mroe performance friendly rudy is extensive and does take some moving things around to get them to work with some mods but the pay off is amazing
If TTW or standalone games what the other posters said Hitmans Enb is amazing Top notch work and the best Enb for quality and performance.
Fallout 4 id recommend The Stalker Enb, the Photorealsim enb and Cinematic Excellence ENB its all up to preference there.
Here are the links to them all so you can comapre what you like and your taste:
Blackout http://www.nexusmods.com/newvegas/mods/48203/? Just put the files in the same way you would in NV
Fallout New vegas
TTW or either game
Enb 47 part to which is linked to above by the other poster
Stalker fx and enb http://www.nexusmods.com/fallout4/mods/86/? Really adds that gloomy feel its my personal favorite
Photorealistic enb http://www.nexusmods.com/fallout4/mods/6796/?
Cinematic Excellence ENB http://www.nexusmods.com/fallout4/mods/95/?
Hope this helps
If you have any questions feel free to PM me as well mate