Boring answer: 10/10 for all of them. I'm not a neanderthal hunter with a lifetime of hunting, making spears, skinning living things, preserving meat in snow, capable of making boats and all that. Any of prehistoric fauna would give me a heart attack, but I'd die of intolerable oxygen concentration before I could see any of them. Food poisoning is guaranteed, and during the first two, there is NO food.
Cambrian: 10000000/10
No oxygen first and foremost, no food since everything is made of cytoplasm, the land is completely barren and has no wood to make boats out (not that I know how to make one). Death here is just as certain as death on Mars.
Ordovician: 1000/10
The carbon dioxide concentration is too high for a human to be able to live here, land is barren and without wood, sea level is too vast for anyone to swim here, animals are likely indigestible and too small to sustain humans, and there were likely some natural disasters too.
Silurian: 6/10
Apparently, Silurian had 14-28% oxygen atmosphere, which 21 percent of human-breathable oxygen concentration is within, leaving some narrow chance of not choking to death. Wikipedia says its climate was stable and warm, and the fauna here is not full of giant predators.
Devonian: 9.5/10
Again with the deadly atmosphere, marine fauna starts being actually dangerous, although the appearance of trees is nice and there is no actual land predators to worry about.
Carboniferous: 10/10 (5/10 without toxic atmosphere)
Ignoring 30% oxygen concentration, big anthropoids and frogs seem like a pure nightmare fuel but beyond that, human is at massive advantage since he is a warm-blooded creature that can attack cold-blooded animals early in the morning, not to mention that viruses would not be adapted to warm-blooded creatures.
Permian: 12/10
The atmosphere stays toxic, and the entire world is a blistering-hot desert (which get super cold at night) full of big carnivorous crocodile/komodo dragon-like reptiles. Ironically more likely to survive than in Cambrian, but still.