With the Gauss Rifle and Chinese Stealth armor, no enemies pose a serious threat. The Gauss Rifle does massive damage (I use a repair mod that changes its repair list, so it can be maintained in good condition), has great accuracy at long ranges, and knocks enemies down on critical hits. Combine this with the Chinese Stealth Armor (which allows high-Sneak players to remain undetected--even in daytime, in plain sight of high-Perception enemies), and it's quite easy to score multiple Sneak attacks against the same target.

Not many enemies can withstand repeated Sneak headshots from a Gauss Rifle.

Edit: For the record, with high Energy Weapons and Repair skills, Deathclaws go down in one of the aforementioned hits. Feral Ghoul Reavers take three. I play on Hard difficulty.

Feral Ghoul Reavers are a pain.

I can deal with them though. Put a few good shots (about a round's worth with Blackhawk) into them BEFORE going into V.A.T.S. and they're doable in one V.A.T.S. round.

Feral Ghoul Reavers.

44 scoped magnam drops those [censored] in one head shot

I wish, lol. These are super ghouls we're talking about here. Not the normal ones. I can shoot them in the head with the Terrible Shotgun with my barrel literally touching their forehead, and they barely feel a scratch. Not the best tactic to use.

again the reavers but now i use the nova plasma pistol and stealth to take them out in one shot or two or three without stealth there not as bad.

I haven't been around Reavers much yet so the hardest for me are those Microfusion Cell sponges called Albino Radscorpions. One time I saw a fight between a Deathclaw and an Albino. The Albino put the smack-down on the Deathclaw and still had plenty of health left over. It took five shots from the Gauss Rifle to finally put it down. I'm glad I took the time to put an extended clip on my Gauss Rifle.

Feral Ghoul Reavers at point lookout

I use MMM, so the hardest I've come across are the PACKS of Super Mutant Behemoths and Gargantuans I come across far too frequently.

The only thing I've encountered and haven't been able to kill was a Reaver. I was in Point Lookout when I encountered my first one, shooting it just drew attention to me, and it ran up and killed me.

I've never encountered an Albino, so I dunno about them.

Oh God, that first Reaver Encounter is a [censored]. It's like, "hey look, Feral Ghoul, you guys go down in one hit! Screw You buddy! Haha! "Then you shoot it. At Point Blank. With a Double Barreled Shotgun. And nothing happens.

I remember running around in circles, shooting it with that shotgun. Laying mines behind me, throwing grenades at it. And popping TONS of stims. For at least a full minute just thinking "OH GOD WHY WON'T YOU DIE?!?!"
Then it finally goes down and, since it was in Point Lookout right after a somewhat major plot point I thought it was a special boss. I was rejoicing in it's death just thinking how awesome I was. Being all, "oh yeah, I rock!"

Then I saw another one about half an hour later and realized it was just a normal new enemy in the spawn lists.