I would say definitely commission on player losses.
If you intend on making serious cash, and don’t mind promoting that casino for an extended period of time (3-12 months)… you will find that your revenue will be quite good in 6-12 months.
Its not unusual for affiliates to make 10-20K, even after they stop sending players to a casino.
I would advise that you go with a casino affiliate program that has been around for a number of years. You don’t want find that your hard work in building up a commission stream only gets burnt because the casino shuts down.
I would also go with a casino that really promotes to their players, and develops their players into being repeat depositors.