So, now Saber, Rider, Archer, and Berserker remains.
Because I'm so bored right now, let's speculate on the servants's abilities (ignoring thei master's), based on what has been shown so far:
Berserker has the ability to turn every weapon he touched to his NP. And he has the ungodly skills to wield them to boot. This is a natural counter for Archer's Gate of Babylon because Berserker can turn Archer's own weapon against him, so I suspect that Berserker has a fairly high chance in offing Archer.
However, Berserker will not do as good when fighting Rider, because of IH. If Berserker got in IH without preparing some weapons beforehand, he'll have to steal one from one of the soldiers there, and it's no easy task to do barehanded (and considering the soldiers are all on the level of Heroic Spirits). But, Archer's Gate of Babylon is the perfect counter for IH, because he can shoot them all simultaneously and the soldiers could do little about it, and because Archer has virtually unlimited supply of weapons to throw with.
So it's a rock-scissors-paper game (Berserker-Archer-Rider) for the three of them. Saber could potentially kill any one of them with her Excalibur, and she possesses the best hand-to-hand fighting skills, Berserker aside. None of the other three has obvious advantages against Saber like those three have against each other.
Now let's see what happens when we add the Masters to the equation. Kiritsugu would probably make a similar analysis to the one I just made and order Saber to stand by and let the other three kill themselves first, and also to recover energy used in that Excalibur. Waver would probably hesitate to attack Saber because of their past cooperation, so he might aim for the other two: Berserker or Archer. Kirei probably won't go after Kariya personally and will look for a one-on-one showdown with Kiritsugu. Maybe he would stage a scene so Rider and Berserker fight each other, then move in to kill the victor. Kariya, well, he's mad, and probably will dance around as Kirei wanted him to. The way the tension builds up until now, the last battle just has to be between Kirei and Kiritsugu.
So, I think the next one to die might be Rider or Berserker. But, considering Rider already has more character development than Berserker, he might go out first. Unless, the few next episode focus on expanding Berserker. Besides, if Waver, the prodigy eager on proving himself, can make it into the last three only to fail, that would make for a very Gen-ish tragedy
Also, pay no attention to this post, I'm just blabbering non-sense out of boredom
