The hardest EB by far for a scrapper is Nosferatu, who is in one of the ouroboros arcs, he is a fifth column EB (council).
On weakest enemies.... warriors have no mez, just lethal and smash damage mainly... so if your highly resistant to lethal/smash, then ramp up the difficulty on them.
Main 50 & Badger Nine Claws Claws/Regen/Body
Other 50's Ph10x Brute Unjust Law Tanker Samantha Urai Scrapper Codename 1250 Scrapper
Cepheus Defender Nilus Scrapper Electro Field Blaster S.PONGE Tanker
I didn't have much issue with Nos on my Claw/Willpower...... or any other EB.
Foe wise I cursed anything that slowed me (cause I like stacking followup) and Malta have -regen (their big robots do, a silly amount, I mean stupid, no really silly) so I didn't like them
Freaks are easy with Claw/WP, early on trolls were a walk through. I really didn't find anything too tough on Claw/WP if you exclude the damned Malta, oh and if Posi hits you with LR and EMP it's nasty, very nasty. But he has to hit and as an EB he dies pretty damned fast
"Well, they found my diary today.
They were appropriately appalled
at the discovery of the eight victims
They're now putting it all together.
Women wrapped in silk
with one leg missing
Eight legs, one body, silk,
spider, brilliant!"
TBH unless you are running every mission from lvl 2 up on INV, you shouldn't have any troubles.
Juat take the first 10-20 levels to get to know what you can and can't handle.
The only thing I have ever had issue with (on my DM/DA) is the nin/nin in the PI safeguard when on INV. A couple of times it's been touch and go, but pop a few insps and it's fine.
I find the Carnies incredibly annoying on my Regens. Not because they're hard, no, they're [censored] easy, but because they go down so quickly they drain your endurance like maaaaad.
The only EB so far I had trouble with was the Positron Automaton from one of the Rikti War Zone contacts... for some reason I just couldn't take him down as easily as all the other EB's.
As for Claws: Yay, great powerset! Good, quick damage and great mitigation, because you can keep your enemy on his back permanently with 3 knockdown/back powers.
As for Willpower: Yay, great powerset! Quite heavy on the endurance (four toggles), but Quick Recovery more than makes up for this, and since Claws isn't very heavy on the endurance, you should be fine. You can handle a lot of enemies at once, because you can get tons of regeneration with Rise to the Challenge.
Good luck and have fun 
The only ones that I find annoying are CoT; all the slows (Quicksand) and the accuracy debuffs.
I was doing a mish the other night on my Dark/Dark and after 5 minutes decided to quit it - it simply wasn't fun - taking forever and very slow xp.
L50s: Tanks: Cryofission - Ice/EM - Dr Celsius - Fire/Ice - Saint George - SD/SS | Controllers: Psichosis - Ill/Kin - Major Chaos - Ill/Stm | Scrappers - Neutron Crusader - DM/SR
Currently Levelling: Angelic Blade - BS/WP Scrapper | Seeds of Destruction - Plant/Kin Controller
Hardest: rularuu and nemesis
Easiest: freaks, Praetorian bots
@False Fiction - Virtue / Defiant
Current projects - [Glaciologist - Ill/Cold Troller] [Cloudshaper - Storm/Dark Def] [Harald Wartooth - Elec/Psi Domi]
Tsoo. They're probably my favourite enemy group, but they're one of the less straightforward ones. Think of them as a melee focused prototype for The Malta Group.
Sorcerers will port in and out healing the rest of the gang whilst debuffing your tohit with their Hurricane something fierce, so take them out first if you can. Then you've got the Green Ink Men wailing on you, not much of a threat individually but get enough of them together and they'll be able to stack their stuns enough to overcome your mez protection and drop your toggles, so be careful with them. Enforcers will drop caltrops, which are annoying if not really much of problem.
Once you get up to Red Ink men and higher they'll start using Kinetics powers on you, and there's one particular Boss Type I've encountered that claims he's only doing siphon speed and siphon power on you, but given the way the power buffs his buddies and not just himself when he uses it I suspect it's actually something a bit more exotic than that.
Like I said, I like 'em, but sometimes you need to think a bit when fighting them
[ QUOTE ]
Once you get up to Red Ink men and higher they'll start using Kinetics powers on you, and there's one particular Boss Type I've encountered that claims he's only doing siphon speed and siphon power on you, but given the way the power buffs his buddies and not just himself when he uses it I suspect it's actually something a bit more exotic than that.
[/ QUOTE ]
Siphon Power buffs those around you.
I'd say the ones my Scrappers (Kat/Inv & Claws/SR, others are too low) find difficult are:
Tsoo (DeBuffs galore)
Rularuu (even more DeBuffs and stupid ToHit)
Council & Malta (high lethal res robots)
Rikti (Drones for the unwillingness to enter melee and high ToHit)
Nemesis (silly range and vengeance)
Easiest - anything else 
@Jay Leon Hart
Kerensky: this has nothing to do with underwear
Zwillinger: I put on my robe and wizard hat...
Synapse: I had to resist starting my last post off with "Yo dawg!"
Flitz (MA/SR) always had a hard time with:
Silver Mantis
Rularuu
Carnie Ring Mistresses
Shivan bosses
Suspect a lot of them do -def, making it easier for them to hit a /SR toon.
UNION @Flitz 50, Lead Hose 50, Red Rag 50
DEFIANT Rose Bloodthorn 34
VIGILANCE Captain Caledonia 20 - Yeah, I made toons on the French server coz we only had 4 back then (might have to transfer/recreate them on one of the US servers)
..and many more!
I'm new to this game, and I'm looking for a little advice. After a few false starts, I've finally started leveling up a main character, a Claws/WP scrapper. Are there any particular enemy groups that are particularly tough with this AT? Or easy? I'm trying to avoid power-leveling and play as much content as I can, but it's good to know which missions I can afford to crank the difficulty on, and which ones I should tone it down a level or two.