steve,
You've got a nice collection there.
I'll give my take on your questions.
Disclaimer: I am a fan of Saigas. And I have made negative comments regarding Ruger for past politices, but not quality of the firearms. (I do have a 10/22.)
I *personally* would choose the Saiga 7.62x39. As I look over your collection, I see the required "AK" slot strangely empty. A saiga is a fine AK to fill that slot with in terms of build quality and accuracy. It will give the reliability of any AK.
However, I do recommend that you convert it to its traditional form-- or buy one pre-converted. I say this because it would be adventageous to have one where a bullet guide has been installed in order to use common AK magazines. If you convert yourself, you can get an easy bullet guide kit from Dinzag's website.
I don't know a great deal about the Ruger Mini-30. But I suspect that it would not fill the role an AK fills as reliabily.
However, I have to ask. What size is your AR-15? I've posted quite a bit on SHTF in the past. Likey, you already have a decent SHTF rifle in that AR-15. I could see why you may want another rifle if you had a 20" or 24" barrel on the AR-15, but if you have a carbine length, it would likely do fine.
From the SHTF scenerios that I have considered, and the one I lived through, likely any fairly accurate and reliable firearm would work. A handgun will be with you FAR more than any long gun.
I would only add that if I did NOT have ammunition stacked deep for at least one or two of your firearms, I'd do that before adding another one in the mix.
-- John