I find that a lot of people think Saber from Fate Stay Night is the strongest servant. Even without getting into who the best servant in Fate Grand Order, I don’t think that is entirely accurate.
The strongest servant in FSN is Gilgamesh bar none. He’s is easily the strongest servant period. In fact, Kinoko Nasu has confirmed this numerous times.
Not even Saber Alter can take on Gilgamesh at full strength (almost positive that saber alter cannot use avalon, which gives her an even bigger disadvantage).
Which is saying a lot.
I don’t think we can undersell how powerful Avalon makes Saber, so the power that would add to Saber Alter is astounding to say the least.
Saber is stronger than SN Archer but that’s just because she has Avalon. Without her ability to use Avalon, Archer at maximum strength could possibly beat Saber, because of how insanely powerful UBW is and his Crane Wing Three Realm.
Even then though, it’d be a disadvantageous fight for him but the possibility does exist in a straight 1v1 match.
Furthermore I don’t understand the people who think that Saber Alter isn’t more powerful than regular Saber. Saber Alter makes Berserker look like a child in comparison.
From a statistical standpoint, she’s pretty freaking insane and has unlimited mana to boot. I hear a lot of people say that her Alter form is a statistical downgrade but it’s actually a very blatant super powered evil side.
I think that’s the whole point of the transformation. Why else would Saber Alter even exist if she wasn’t more powerful?
Ultimately it doesn’t matter that much, because in the end, not including the stat differences and gimmicks that are included in Fate Grand Order, Gilgamesh is easily, hands down, the strongest servant in Fate Stay/Night and potentially the entire fate franchise as a whole.