I usually go in another Fallout's forum, but i was recently lurking in this one looking for new discussion thread i got interested in this one :
http://www.gamesas.com/topic/1494271-lore-wise-who-are-the-strongest-soldiers/
After i read all you argument, it got me thinking on the subject and register to answer.
I've seen that it was unfortunally locked, but from what i understood, it was mostly about a number of post limit, than an unapropriate topic.
I think that it is a weird regulation, since they usually fuse thread that deal with the same topic in other forums, but i am not here to make regulations, since i just arrived.
So, if the topic is not forbidden, let me share my 50 cents on the subject.
Obviously, there won't be any clear winner. If we talked about pure fact, the thread would be over on a single page, when the fact had been said. That's the fact there is no clear answer that would keep us entertained.
I fairly agree that the best contenders are the NCR veterans, the 1st recon, the legates, the Praetorians, the centurions and the Enclave remnants.
Those have been mostly agreed by everyone.
About the Securitron and the Brotherhood of Steel...
I would say that the Securitron would be able to slaughter easily any unprepared soldiers.
But with some skills, some range, those piece of metal would show their limits.
You can program some awesome A.I., they would remain A.I. in the end of the day. They could adapt in some situations, but won't go much beyond their programing, and would show some limits, while the humans would endlessly adapt. Also, unlike the Calculator's army, All securitrons are all the same generic model. So if you manage to kill one using one strategy, chances are that you will be able to beat all the other securitrons with that very exact same strategy. Also, all securitrons would have the sames flaws. Learn to study those flaws and you will win 100% of the time. You may, although, suffer some losses in the beginning, while learning those flaws, losses that you may not be ready to accept.
Also, they have probably limited shooting range, limited senses, limited abilities to move that be aknowledged, and that would never change since there is none to build or improve them, no Calculator, no engineer, no scientist.
They are also 100% vulnerable to EMP. They can also be reprogramed by the followers or the Brotherhood of Steel.
So even if they are quite strong they cannot be the ultimate winner. They will always be someone able to take them down.
The Brotherhood Of Steel, on the other hand, can adapt, make babies, study weapons, make new ones, they have elder and paladins to coordinate troops, think of new strategies. They have spies to gather informations on the ennemies, as shown in Fo2 & FoNV. They would definitaly have some EMP to beat securitrons quite easily. Also, their regular troops, having better gear, some hard training, and mindset to beat any other regular troops. Of course, not all of them are champions or veterans. Some of them are initiate that just trained and never been in a real battleground. Those would certainly be beaten by any elite troops like the NCR veterans or the Praetorians. But they also have some real badass too. Take Elijah, Rhombus, the warrior from tactics or the Lyons Pride. Those have seen many more battle than the usual grunts, have many skills, a lot of experience and the ability to adapt. I am not saying that they would win easily agains't anyone, but they would probably able to handle themselves agains't an NCR veteran or a Centurion, agains't ennemies that would easily kill some Brotherhood of steel regular initiates. They would also have their chances agains't Enclave Remnants as those people are quite the same, with better gear. After all, the Enclave Remnants are also some veterans/elite troops, not just regular grunts, that, we could assume, would have died far before. So, IMO, the BOS veterans shoud absolutly appear on a best soldiers list.
Also, i assume that even a regular Brotherhood of Steel member should be able to beat an NCR heavy trooper, wearing Power armor, as the BOS members would benefit from decades of knowledge and training, while the NCR members would just get the armor, with nothing more than a few advices.
Also, if the thread is more about lore than Gameplay, i think the west-coast super-mutants deserve some credits.
Gameplay-wise, in any games, the super-mutants is far weaker than any heavily armored warriors, because of their lower damage resistance, and, in older games, their unability to run. But Lore-wise, they have always been a force to be reckoned with.
I will use spoiler balise for previous games plot-points.
If you let the time move on, the super-mutants would beat the Brotherhood of Steel in Fallout 1. (the fight won't be seen, but the base would be destroyed) They would also beat everyone else.
In Fallout 2, the Melchior's group managed to beat the Enclave. (to be fair, they outnumbered them)
In Fallout tactics, they managed to sustain for a three way war for a while, agains't the BOS and the Calculator's army, the main protagonist and the main antagonist armies of the whole games.
Before Fallout 2, you had Jacob, a paladin of the Brotherhood of Steel, considered as an efficient warrior. The guy spent entire days trying to kill Marcus, an intelligent super-mutants, never to succeed. In the end, they made peace and built a town.
Many plot points of Fallout Tactics and Fallout:Brotherhood of Steel were the BOS trying to counter the remnant of the Master army to rise again, fearing the potential of that group.
So even if they are weaker gameplay-wise, they are considered as very strong, lore-wise. If they are still feared by every normies and ghouls, it means something. Also, like any other groups, they also have good and bad troops. They have warriors, and people that wish they never been dipped into the vats. They have dumb guys and smart guys. They have regular troops, and nightkins, that are like special ops with stealth boys. I am not 100% certain that you could add them in the "Best soldiers" list, but it have to be considered, if you pick a Nightkin that can infiltrate any place, that remained as intelligent & strong as Lou or Marcus, that managed to stay sane, by not overusing stealth boy, that kept training in case the unity would rise again. Whether i am a BOS paladin or an Enclave remnant, i would definitally not want to cross his path.
About Deathclaws, it is hard to say. Gameplay-wise, they are hugely strong, maybe stronger that super-mutants, but lore-wise, i don't think they have much fame. They were feared in Fallout 1, while they were quite rare and unknown. But after that, i have not seen any non-soldier that would actually fear it. The Enclave torn them to pieces in Fallout 2, while in Fallout:Tactics they don't have the opportunity to fight any other soldier than the BOS that beat them, and the Beastlords, that only appeared at that specific time of the Fallout universe, and have not the time to be compared to anything else. So, basically, lore-wise any group that have well-trained soldiers is not supposed to be afraid of them, even if, ingame, they would have chances to beat them.
So basically, i think the contest should involve Legates, praetorians, centurions, NCR veterans, 1st recon, Brotherhood Elite soldiers, Enclave Elite soldiers, and the best Nightkin that had managed to stay sane and kept training.
I thing the Calculator's army could do well too, but they are not a Mojave faction. But i doubt that they would beat the elite guys, because of their A.I. limits.