Ok, I have had a few votes and it is close. # for Ape planet and 2 for Rhino Planet.
Here are my thoughts. The 3 planets ( Feline Planet (Katz) Rhino Planet (Rhozch) Ape Planet (Dirth) ) circle the same star (Sun). Rhozch and Dirth are very similar to Earth, Katz is further away and is a very cold planet. The Felines are very intelligent and developed quickly using space travel to rule all three planets. Depending on which planet the ship visits first is dependent on the problems they will have when on the planet.
1. Katz is frigid. The main characters will most likely have more trouble with the weather.
2. Rhozch is a planet of working Rhino's (Mainly) and they are the brawn of the three worlds. They are easily conquered so the problem could be related to the working class versus the Feline upper class who exploits their labor.
3. Dirth is mostly wilderness and jungle. The Apes are very free and do not readily submit to Felines. The possible problem here could be a war with the felines.
Choose wisely, I will be starting a new chapter by the 2nd week of March.