Unfortunately, there’s no statistical data because there are so many slots and their results are so random that it’s rather difficult and even utterly impossible to analyze how financially rewarding they are. Nevertheless, there’s a RTP (return to player) Percentage that you can check specifically for a slot that interests you most. If the slot’s RTP is higher than 85%, it’s absolutely worth playing! Evidently, the higher RTP, the better. Yet, you still need to bear in mind that there’s absolutely no guarantee that you’ll win anything at all, so you need to gamble first of all merely for fun, not to rely on gambling as your source of income, and never spend on gambling more than you can afford. Check the list of best free slots and their RTP - Cleopatra 95.02%, Gonzo’s Quest 96.00%, Monopoly Slot 95.02%, Mega Moolah 88.12%, Starburst 96.10%. As you can see, the RTP of all these slots are higher than 85%, which means that they all are absolutely safe to play.