For me, it'd be Hunting Rifle, cause living out in Oklahoma and right on the border of Texas. Hunting is a tradition, plus the huntin rifle is so powerful with the mods on it as well. And for Fallout 3 it was chinese Assault Rifle, cause who doesnt like waking their parents up at 1 in the morning for firing that bad boy. but im curious about you guys and what weapons yall used before mods.

The silenced 10mm i got from Mr. Burke, sure it was weak but it let me roleplay as a secret agent on the Xbox 360 before i upgraded to a PC and could use mods.

For New Vegas it was the Assault Carbine and the Anti-Material Rifle, For Fallout 3 It was definitely the CAR and a Laser Rifle.

In New Vegas, I tended to use Maria more than often. Its elegant engravings and grips made it easily one of my favorite weapons in the game.

I haven't played Fallout 3 in quite a while, but I definitely recall the Lincoln's Repeater being my go-to choice. The sound effects on that thing were amazing, and the reload animations were really unique compared to anything else in the vanilla game.

Before I modded, and played Fallout 3 on the Xbox 360 I used this exploit on Operation:Anchorage that would give the player a Chinese Assault rifle with infinite health as well as all other guns in the game and 30,000+ round of ammo. In New Vegas, I went towards the cowboy guns. Those weapons, even in vanilla had really nice textures and animations. For some reason the design of the service rifle/assault carbine just looked too off for me. Like the guys at Obsidian knew what an AR-15 looked like buy only silhouettes and I got this uncanny valley effect when looking at those rifles. That's not even mentioning the nice energy weapons in both games.

The hunting rifle, it's just so damn versatile and you get it pretty early in both games. I've used it almost every playthrough tbh, nothing beats the good ol' huntin rifle 8|

In new vegas i used "That gun" the most. In 3 i mainly use hunting rifle.

For base game weapons, I used the Assault Carbine, Hunting Rifle with the attachments, and This Machine before the GRA DLC came out with the Battle Rifle. For Fallout 3 it would be the Assault Rifle and the Chinese Assault Rifle

New Vegas: .357 Revolver
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3: Hunting Rifle

I'm a cowboy at heart. =p

3: chinese AR
NV: Anti Material rifle or the BAR

I loved the survivalists rifle. That was in the dlc honest hearts. It was appropriately damaged and incredible reliable, the only thing that was off was the damaged iron sights.

In 3 I like the chinese assault rifle, combat shotty and/or sniper rifle. Or the named versions of said weapons.
In NV it's the hunting rifle with mods. It is a good all round weapon. Except fer the Death Claws in NV. Anti material rifle is my go to fer them as .50 cal ammo is expensive so I save it fer the nasty beasties. 

Oh and not to forget That Gun. Because it's THAT GUN.

Just the Combat shotgun in FO3, then in New Vegas probably This Machine because I just love Historical weaponry

I admit, in NV I mostly used the GRA Sniper Rifle because it was, you know, OP. In Fallout 3 it was Lincoln's Repetear.

For me in New Vegas is the All-American all the way, well once I obtained it that is. In Fallout 3 it Lincoln's Repeater.

When I started playing New Vegas, I started off using the 10mm SMG as my go to weapon since it widely available and had very common ammo, when I get in higher levels, my final main weapons where Maria, Anti-Material Rifle, Hunting Rifle, Gobi Campaign Sniper Rifle and the Hunting Revolver.

Currently am sticking more to a Hunting Rifle using it in TTW, served me very well in both wastelands.

In New Vegas it was definitely This Machine, it was by far the most unique weapon in New Vegas for me and it certainly wasn't a weak rifle either so it was great all around to use. But that was before I was able to play with mods. Once that happened all I use is the HK416 from the BF4 weapon pack on this site.

Sniper Rifle and Gauss Rifle. I was disappointed to see that they changed the sniper rifle and gauss rifle in FO4, from what they were in previous games. Thank the maker for mods lol.

I always used the Hunting Rifle or the unique version of it with a new texture and the 10mm pistol as a sidearm.