1. Firestar - Firestar is still quite the warrior even at normal levels, but when pushed against a wall, Firestar is truly at his best. It can be said that a difficult situation is in fact an optimal one for someone like him, who has killed the likes of Tigerstar even while fatally wounded because he just refused to die.
2. Scourge - The strongest without question under ordinary circumstances, one so deadly that he cannot be beaten in a straight fight but with trickery instead by exploiting his bloodlust. His attacking power is high, his agility is constantly praised, and he's basically just a whirl of razor blades so trying to attack him is dangerous too.
3. Tigerstar - The original strongest warrior, and would probably be Firestar's equal if it weren't for Firestar's off the wall adrenaline moments. Still, he's huge, strong and tough and his only deficiency is being a bit cocky and maybe unagile.
4. Bramblestar and Hawkfrost - These two are basically clones of each other and have those good old Tigerstar genes only slightly diluted. Even if they have slightly less strength than their dad, they're still very strong and tough along with having great combat skill as not just any cat can break necks like that.
5. Hollyleaf - She went blow for blow with Hawkfrost and even wounded him badly enough that he sought to retreat. Strength I don't believe is her forte so much as a berserker fighting style where she takes on a mindset of "you might kill me but I will kill you in the process", which has its own advantages.
6. Graystripe - He's quite a powerful brute, being so strong he kills Clawface practically by accident and ragdolling cats in a few battles. He's got a whole lot of bulk to him and the fat probably helps defend him too, even if it slows him down.
7. Ivypool - Noted to have potential by Tigerstar, she is probably the most successful trainee of the Dark Forest. She doesn't have much strength to leverage, but her agility is high and her skills nigh mystical in terms of how effective they are sometimes.
8. Cloudtail - He's noted to have great potential even as an apprentice and was able to fend off Scourge while his uncle healed thanks to his determination and grit. While he seems to lack the skill of some warriors, his toughness and pitbull attitude really make him a difficult customer to take down in his prime.
9. Brightheart - While exploiting how others underestimate her, Brightheart has brought down cats much stronger than her with surprising efficiency and shown herself to be deadly fierce on the defensive. Her weapon is causing cats to underestimate her, so it's a little gimmicky and that's why she's so far up along with a lack of great stats.
10. Blackstar/Bone - Big, tough, and thick as a brick, that describes these two black and white deputies. Still, the pair of them prove that with brute strength you can accomplish many things. Blackfoot's on par with Bone despite Bone's dogtooth claws solely for that scene where he kills Reedwillow by ripping his chest open.
Honorable Mention. Yellowfang - She did fend off Blackfoot by exploiting his straightforward style and broke Brokenstar's neck easily, no small feat. I think she benefits most when she knows someone's style in advance so she can exploit the holes in it viciously.
????. Lionblaze - I have no idea where to put this guy. Sometimes, Ashfur is pummeling him. Sometimes, he's lifting trees. Sometimes, Shredtail is pummeling him. Sometimes, he takes on armies of cats with no problem. At his best, he's number 1 or 2, at his worst he's jobbing like he's not even breaking into the top ten.
As far as Darktail goes, he never impressed me really. Holding down cats to drown isn't impressive when he has his whole gang of groupies right there to help weaken the cat before throwing them in the drink or else help him hold them down. He beat up Rain, sure, but Rain was just kind of a big rogue with nothing else to his name and the way Darktail killed him didn't scream amazing to me either. The fact that he went even with a little wuss like Onestar does not help his image either.