which one would it be?

For me, without a doubt, it is the Gobi Campaign Rifle.
There is nothing as versatile as this lovely tool.
Currently I'm playing LR for the first time, and with the exception of the Courier Mile, where i could bring the Red Glare to *really* good use, it's Gobi carrying me through all the time.
Here's the summary of upsides:

+ excellent long range weapon
+ good base damage
+ crit multiplier
+ very high crit bonus, especially with Better Criticals, sneak crits a DC Alpha in one shot
+ good ROF
+ low AP cost of just 24, making it a very good medium and short range weapon, too
+ good durability, even with the Built to Destroy trait
+ ammo is common and easy to obtain in numbers
+ powerful Hand Loader ammo
+ with a little bit of skill beelining, it is theoretically available very early on

If that doesn't read like the ultimate All Purpose Combat Tool, I don't what should.
That said, i have to mention, I'm playing on Normal difficulty, HC and I put some efforts into enhancing my base critical hit chance(it's >20).
Playing on my conditions, it is an absolute powerhouse beyond any means.
Sure, you'll find a weapon that will excel the Gobi in almost every department, but as a package, there's nothing as complete and well rounded.

So what about you people?

All American. Gobi's better when using VATS, but AA does the job when low on AP.

If I were going Guns, I'd pick the Bozar. Multimission capability is pretty much it's only stock in trade. But as a Melee/Unarmed player, I choose the Shovel. Sure, some people are going to say "Go all the way and get Oh Baby!" but you really can't beat the Shovel.

+ Guaranteed knockback VATS move(no matter what target)
+ Good base DAM
+ Good base ROF
+ ROF can be improved significantly with perks
+ DAM can be improved significantly with perks
+ Gains Armor Piercing effects, Knockback, & passively improves DT with perks
+ Silent
+ Can poison targets
+ No need for "ammo"
+ Takes down a lone DC Alpha regardless of combat situation
+ Excellent durability
+ Lightweight(3.00)
+ Can open graves

In short, the Shovel, like most Melee/Unarmed weapons, levels with you. At the end of it's leveling, especially supported by Chems, it's pretty much all-powerful. You can find weapons with better DAM & ROF, weapons that can be snuck into casinos, weapons with better crit abilities, but the Shovel is a lot more powerful than is intuitive.

-Nukeknockout

All-American, not necessarily because it's the best, but because it's versatile - a sniper rifle is not ideal at facehug ranges, and the riot shotgun is not ideal at long ranges. Ammo is also pretty easy to find, and comes in (at least) three types.

Alternatively, Pushy if I'm going unarmed. It's hilarious in use, but also practical in most situations.

For Guns I'd go with the CZ57 Avenger because it has the highest base spread of any automatic Gun, has the highest DPS of any weapon in the game and standard 5mm rounds come with the very handy -10 DT.

For Energy Weapons I'd go with a fully upgraded GRA Plasma Defender with Optimized Energy Cells. It decimates Legion Assassins.

Just one weapon?

Assault carbine. Requirements are not too high so it's ok to start with, ammo is plentiful, and it can handle any enemy in the game.

The Lobotomite: Avenger? Really? How would it handle at low levels, and how would you keep it fed?

Holorifle, I'd say. If not that, a Laser Rifle, fully modded.

Trail carbine.

The Plasma Defender is where I was being practical and if I had to choose one then it would be this one.

I really only mentioned the Avenger because I'm madly in love with it.

Hunting Rifle. It has a good range, not bad damage, and the ammo for it is available more or less at every level.

Ranger Sequoia because of the Brush Guns glitchy misses/inconsistency in VATS. I love the damage the brush gun does, but i'm tired of missing 95% hit changes in VATS with it. I never miss with the Ranger Sequoia and it packs a nice punch. Really easy to get from the dude in Camp Golf (stealth melee kill) and I have no problem stocking up on the ammo and converting to hand load. I usually have well over 1,000 rounds of .45-70 hand load ammo after 10 to 12 hours of gameplay. Decent range(not as good as scoped rifles obviously) for a revolver. The RS looks pretty sweet when you are blowing off peoples heads in VATS too. Dirty Harry would be proud.

You could easily feed the CZ57 by going with Barter, Sneak, & Speech until you're skilled enough with enough ammo to use it right. I also think putting points in Unarmed would be a given.

-Nukeknockout

Vanilla: All-American
DLC: Holorifle
Mod: SAKO RK-95 Tp (stat wise it's a beefed-up Assault Carbine with large caliber, silencer and scope as modifications)

CZ57 Primarily because its close range, as well as high fire rate and quick to relode. As well as extended ammunition hold.

Apart from that, give trusty Raul my Anti-Material Rifle (Boone would do better, but seeing how Raul and Lilly are the only ones I have left.. yeah.... ) and hook up with Rex.

I don't believe you didn't say anything about giving your companions weapons.

x)

Damn, I wish that last gun was available for real on the ps3. That gun sounds awesome.

Flare Gun.


Cause it's a flare gun.

That takes TEN flamer fuel to shoot ONCE!

This aside, I have to agree that it is a Flare Gun which makes this problem irrelevant at levels 1 through 10.

Survivalists Rifle

Ammo is expensive, but damn is it versatile. I just love it.

Well FF is pretty easy to get a hold of through merchants so it's not much of a concern to me.

Flamethrower (unlimited ammo) or the Recharable Assault Riffle with non deterarating weapons.

Riot Shotgun. Nothing will survive a forward charge against a Riot Shotgun with Shotgun Surgeon perk. And I like that you can breakdown 20gauge to make all sorts of 12 gauge ammo for it. High DPS and DMG,insane ROF, Large ammo drum (12 shots) Nothing has worked better for me when ive been rushed by Deathclaws, Yao Guai, or the spore people. With a little jet or similar chem/aid you can easily get off 4 to 5 shots in VATS . Ive often killed groups of 3 dangerous mobs at close range just going from VATS to VATS on each one. If you have Grim reaper sprint perk, Its even more deadly at close range. (Dont have GRS in this playthrough though and probably wont get it as it turns you r game into a VATS fest and makes gettign multiple kills in a row too easy.

Mercy. Nothing can withstand it with the explosive perks maxxed out, plus the one to take less damage yourself.

Knock-Knock only because I could cut my dinner better with that than with Oh Baby!

http://www.majkasvihoruzja.com/files/slike/puska-sako_rk_95_tp_2.jpg. The best AK-47 derivative in the world. Even a deadeye like me, who needs glasses but can't use them when shooting, scored pretty nice shots with that beauty.

Perforator!! But alas is not in NV so fully modded laser rifle if playing an energy specialist or Ratslayer if guns. It's not that powerful at high levels but is still a great gun