Strangers in paradise - C. Anvil

The first settlers on the planet Paradise were to create a deep-space heaven, a model for all
other worlds. But the great experiment failed. The great capital city of Paradise lay stinking in the sun, its streets overrun by monstrous rats, its rulers corrupt and indifferent. This was the strange world the three men from the Interstellar Patrol found when they crash-landed their ship on Paradise. They had made an emergency stop in Hell. Menaced at first by carnivorous plants and huge catlike beasts, the three men fought their way out of the jungle, only to face an even greater danger—the people of Paradise.