At this moment my favorite online casino would be Casino4Dreams. I discovered it by accident on some Russian casino forum, and thought I should give it a try. It is now almost 4 weeks that I play at this casino and I must say I am blown away by the payouts. In first week I didn't win that much, but in next two I was piling up my credit easily... so many winnings I always leave at least 30€ to play and the rest which are fast (the same or the next day).
I can highly recommend it to anyone. At least check it out and see for yourself.