I always loved the anti-material rifle, it's a shame the ammo was expensive as hell though.
Not like caps are a problem in new vegas anyway.

The anti-material rifle was mint at vodka scoping deathclaws in the face, and killing them.

F3 - chinese assault rifle.(just get used to it)
FNV - Magnum 44.(i like it because of Dirty Harry)

Well Nigel, I'd have to go with the anti materiel or the 12.7 mm pistol.

Hmm the Hunting Rifle has always had a place in my hotkeys.
Just add a scope and bam! Its now a sniper! combine that with the Weapon Mod Menu and you have a nicely versatile rifle.

I really love vanilla melee weapons, especially the katana.

my favorite weapon was always the Chinese assault rifle when i use to play on xbox 360 and ps3

My favorite is the Infiltrator, Nothing beats a suppressed AR with a optical sight to boot.

I have to say the xuanlong becuase that chinese ar kicks ass.

My favorite is A Light in Shining Darkness! It's a reliable weapon for me.

The Hunting Rifle...not too strong, not too weak, and the design is perfect for a wasteland/post-nuclear war/Old World setting.

I like Lincoln's repeater if it is a little too powerful.

I also like Terrible Shotgun!

Lincoln's repeater and the 44 magnum. they do the good job (no dirty thoughts)

I'm assuming by vanilla you mean no mods and just game and DLC

Fallout 3: Backwater Rifle from Point Lookout

Reason: I had pretty high luck (8 luck) so the amount of crits I'd receive from this gun would be very punishing. This helped me throughout the DLC itself since the Swamp People have a good amount of health and are pretty hard to kill. In the regular Capital Wasteland, they make quick work with Reavers.

Fallout: New Vegas: Marksman Carbine

Reason: Honestly, I'm not really exactly sure why this is my favorite, but the moment I began using this rifle, I've always enjoyed picking off enemies from a distance with this rifle. The fire rate of this rifle is great but the recoil bothers me a bit.

Can't say I had a favourite in fallout 3, but for fallout New Vegas my favourite would have to be the trail carbine. I just enjoyed the gun and the style of gun it was, 'twas nothing super special or powerful but it brought so much fun specially in the old style it was

I liked the trail carbine, nice choice.
Nigel Farage approves.

The Trail Carbine. Packs the punch to leave the Legion dead by lunch.

Ranger Sequoia. The thing is lethal. No wonder the NCR call it,"The Monster of the West."

The Sawn off shotgun. I know a lot of people hate it because of it's pistol grip/ vanilla animations, but I have always really enjoyed it.

For fallout 3 I would have to say plasma rifle since I liked seeing people turned to goo
And New Vegas i would go for the LAER from the old world. Blue cause it was really OP

For fallout 3 it has to be the Hunting Rifle by farm just had so much charm to it with it's worn and torn look to it with with the wire wrapped around parts along the gun as well as the duct tape.
And with New Vegas it is the lever action rifle it is so bad ass