I think you will find a wide range of answers for this one, but I will share my experiences.
Several casinos have produced whales for me. The one that does so most consistently NOW is English Harbor.
In the past I attracted several Mega Whales at Casino On Net and the highest commission on two of them exceeded $60k in a one month period.
Curiously enough those whales are why I eventually stopped promoting Casino On Net as one player went on to win every month for nearly ten months and cancel out my commissions by all my other players. I went from consistent $12K – $16k a month commissions to being more then $140K in the negative by the time I pulled the plug. Since Tradal carried forward negative balances I didnt see a way to ever get back even as long as this killer whale was in the water.
Aces High at Referback is decent for whales due to their bonus structure and retention team.
My third candidate is Angelciti which is now Shark casino. I have several active whales there now.