I actually own and have shot all 3.
All of them are excellent rifles.
To me, the "ideal" SHTF rifle would be the SCAR 17 because it's harder hitting, better range than the 5.56 rifles.
But you'd also have to consider in your "doomsday" scenario that you'd want to carry as much ammo as possible and also want to scavenge mags and ammo.
If you take those things into consideration, you'd want the SCAR 16 or Tavor because you could scavenge every AR mag.
Between the SCAR 16 & Tavor, the competition is stiff.
The 16 is just awesome, accurate, reliable and sexy.
The Tavor is all the above in a SBR size package.
Today, I'd take the Tavor, ask me tomorrow and it might be another answer.