Depends what you like really. Cassandra is predictable increase in difficulty over time. This is nice for learning game mechanics and practice preparing for harder and harder events. Randy is just random and doesn’t care, which can be as much positive as negative. If you like unpredictable playthrough while knowing how to deal with crisises go with this. Neither is particularly easy/hard, that is much more dependent on the Difficulty you chose. Check out the rimworld wiki on for a breakdown.