Death immediately after birth, regardless of lifespan because the concept of time doesn't exist... to animals, this is still "the land before time".
Constantly living in fear, and no comprehension of my surroundings except for the dumb shit that some tiny animal brain tells me is going on.
Utter and complete irresponsibility for your own actions, no choices about how I act, no hope of change, no awareness of my actions, and no remorse, and no give and no let up.
Constantly pissed off all the time.
No friendships, because my brain is telling me to eat the human.
No knowledge of anything outside of "I'm hungry and I want to eat".
Darwinian law telling me to go kill somebody else's infants because they're future competition for food and mates.
On one hand, Constantly a victim living in utter agony from heat exhaustion, sleep deprivation, fear, injury and disease, and no medical care whatsoever...
And on the other hand... no appreciation for any relief.
That sounds like a pretty rotten shit deal to me :P
So as bad as the human world is, I wouldn't trade it for anything else.