Hunting Rifle with scope and custom action. Or the Brush Gun.

For me it be the La Longue carbine because of it beauty and how fast you can fire with it also because of how much i love being a cowboy in Las Vagas that gun really shows it not the most powerful gun but it nice walk around with

By the time I hit level 50, I just wore my Courier's Duster and carried that at my side. At this point I don't even need to bother, everything just sits down because of that thing!

Joshua Graham's pistol whippin' 45.

Nah, but seriously I would use survivalist rifle, I know I posted here before but I changed my mind.

If they made that melee weapon a whole 10 dollar DLC, I'd buy that.

I also posted in here, but I'm changing my choice to Lucky. Its still my favourite item in the game.

Guns: either Riot Shotgun or LMG (the latter needs the Grunt perk to keep up, though)
EW: Sprtel-Wood 9700 (yeah, it degrades fairly quickly, but Repair Kits are as common as dirt)
Explosives: Annabelle or Mercy (if a Grunt character, then a Grenade Launcher)
Melee: Proton Axe or Proton Inversal Axe
Unarmed: Superheated Saturnite fist

Obviously, these can't really be had at the beginning of the game unless you're on a PC, but they are the ones I try to get ASAP unless the RP demands otherwise.

The Cowboy Repeater.

I cannot believe no one has said Browning Automatic Rifle!!!!!

Yeah. Automatic Rifle. Fully auto .308 rounds? Yes please!

The BAR also has an amazing graphic and sounds awesome when you fire it.

It's a good weapon, true, however any character I would use it on ends up using the LMG or Bozar instead. Then again I'm partial to heavy weapons, so not exactly an unbiased opinion.

The reason nobody has brought it up yet is because of the horrible spread (thank god for j.sawyer mod) and the 12.7 does everything the AR does but better (in vanilla of course).
But indeed it is one of the coolest looking and sounding guns in the game.
mine is 12.7mm SMG, it used to be the assault carbine, but since GRA mods the 12.7 kicks so much ass.

Survivalist beats all the weapons in the game hands down.

MFbreeder Alpha with a high crit build and the appropriate perks also bloody mess thrown in for good measure,should get past any DT, good rate of fire for the most part and never worry about ammo again.

I agree with OP Gobi is great and used it almost exclusevly with my NCR play through for RP. I also did a this machine playthrough and had a great time.