What is better trilostane or mitotane for dogs?

Neither one is better than the other. They both work to control the adrenal gland and they both require careful post administration monitoring. That being equal it boils down to cost and ease of administration to choose one over the other. Mitotane tends to cause necrosis of the adrenal more than trilostane, which would lead the patient into addison's disease. In some respects this is not terrible since the condition is treatable in a similar way as cushings disease. Florinef would simply be substituted for the mitotane. I think addison's disease is better to have anyway if you had a choice.