Once upon a time it was PS, I found it getting less and less enjoyable and about 4 years ago I switched to 888 and haven't regretted it.
Awesome freerolls (now includes 2 CC freerolls per week since I'm Canadian), good promotions, a free daily spin (was 2, but something is wrong with the mobile spin) where you can get good prizes.
Somehow I got Elite status and that has been very good to me with extra goodies.