Hi I want to farm for these two champions so I can level them up. I was wondering which is the best difficulty for that. The ratio for number of turns per 8 units of energy  is 1:1.33:2 for brutal:Hard:Normal. 

Does the probability of getting these champions increase with difficulty as well? Or is it better to go on the Lower difficulty where you will play more games for the energy?

Any advice would be great. Thanks.