There are a lot of slots to choose from, but I recommend Huuuge Diamonds or Phoenix Garden. You should join the club with the most members and/or League Points. Then tap advanced search, and enter the settings like this. I always just play as guest, but I think you get rewards by connecting to Facebook (hardly any though). So here's how I usually do it step by step: The first time I did it I spent $20 and 5 days to finish (lol), but as I kept doing it I got more familiar with the game and went from $20 in 5 days to $0-$5 in one day.
I did each of them about 3 times already, and all of them credited/pended at 150. I'm pretty sure the price changes a lot, from $45 (lowerst) to $55 (highest). So right now Huuuge/Billionaire Casino (they're basically the same game but re branded) is at $55 each. Disclaimer: By 'a day' I mean 8-10 hours straight