I'll go with New Vegas Killer. The dialogue is so funny, and the Boby Bass guy really fits the New Vegas IMO. I recommend that you try the mod. You wont regret it.

My favorite mod of all time belongs to a Skyrim mod. However, my favorite Fallout mod belongs to Project Nevada.

I'd have to agree with Callinoria. Project Nevada just makes the game feel all new again

My favourite gameplay mod is probably Project Nevada. Massive overhaul to the combat and experience system, more items, customisable features (dynamic crosshair, enhanced vision overlays, etc) Makes the game a lot harder, with ways to customise the difficulty.

I have none in particular but Underground hideouts for both NV&F3 and armor mods that are extremly lore friendly

I'm split between Boom to the Moon (an incredible quest mod) and Project Nevada. Both add a lot of great stuff to the game.

Both Underground Hideout mods for FO3 and NV along with Project Nevada for, of course, NV. Each mod adds their own special enhancement whether it be seeing your dwelling become decorated as each quest is completed or becoming roboticized with Project Nevada. It is the little things that really make a big difference.

I'd have to say it's Project Nevada. I don't use it by itself, I complement its Rebalance module with JSawyer and Vicious Wastes. But Project Nevada as a standalone offers a great deal of possibilities, from introducing basic but cool features like visor overlays, grenade hotkeys, slower backpedalling and the like, from giving the user the ability to customize his experience in-game.

I wouldn't be able to play with New Vegas' vanilla gameplay. I just couldn't.

Marts Mutant Mod. The wasteland never feels empty and theirs such a interesting variety of mutant's on top of it.

the battlefield 2142 weapons mod that i had on a hdd and now it's lost to the sands of time, dear god what a mod, stuck in the pit with em, gods above and below it was a delicous time!

My favorite mod of all time is probably MISERY from S.T.A.L.K.E.R. Call of Pripyat.
Love the realism elements and the atmosphere the mod adds into the original game. Makes it feel really immersive.

The Legion Will Ryse, mainly for how it replaces Salt-Upon-Wounds' helmet with Glott's from Ryse: Son of Rome. I downloaded the mod just for that purpose, and Glott's helmet looks much more badass than the vanilla SUW helmet. I have not gone back. I wish it didn't affect Lanius, though; seeing his vanilla helmet on the NCR posters in-game and then fighting him at the end to see him wearing armor from Ryse felt a bit immersion-breaking. (Bear in mind that I've NEVER done a Legion-aligned playthrough.)

Classic Fallout Weapons in New Vegas is another gem. I always felt there weren't enough weapons in FNV, DLCs and all. You'd think we'd get more items from the other games to keep things interesting. Whatever weapons I don't use, I give to my followers.

NCR Overhaul by Dragbody or one his other overhauls. They make the game feel a lot more fresh after playing it countless times.

TTW is probably my ultimate favorite, though; blending together my two favorite games of all time, on top of fixing Fallout 3?? It's absolutely phenomenal.

I would have to say that some of my favourite mods tend to be smaller mods, like utility mods or small animation mods. Companions, 4k textures, weather mods and quest mods are all good in their own right, and I would probably accredit Someguy2000's as the best quest mods available for any of the Fallouts. But in terms of "I cannot play without this mod" I would maybe say something like the eyepatch, Fellout or one of the weapon animation replacers. I think it's the small things all added together that add to the experience as a whoe, rather than one stand out best or favourite mod.

Edit: I acutally thought about this some more since posting this and I think I know what my favourite is. There is a journal mod for TTW that lets you fill a journal with whatever you want. its such a small mod but I've managed to better craft the story I wanted to tell through actually writing down not what I felt, but what my character felt at that time. Having your own branching story arc over the life span of your character's time in the mojave and the capital wasteland. This is probably the most crucial mod to my current playthrough and I don't think it would be the same without it.

For me it would be NMC´s Texture pack it makes the game so much more Pretty and is a must for every Graphic Overhaul Mod List.

Real time settler and wasteland defense. Why buy a player home when you can make your own.

For Fallout new vegas it would go to Solid project and Project nevada cause it gives the game much more feature.

@"Jcramos" Has The Solid Project not been pulled from the nexus? It was giving me some trouble not long ago (Conflict) and I went to the authro's page and I think it was hidden?

All faction overhaul mods by dragbody, I really love the choice of characters. It makes every encounter unique.

Wow, I actually forgot about the 2142 mod... it was for Fallout 3 right. As I recall, the author(s) never finished it, which was a shame.

My favourites were the building mods for FO4. I shamefully spent more time building crazy structures, than actually playing the game. Tried building my own version of Rivet City at the drive-in theatre. It looked like the ship was coming out of that giant screen.