In GTA Online, the best casino game to make money is undoubtedly the "High-Stakes Blackjack." This classic card game offers players the chance to maximize their winnings with strategic betting and skillful play. With a low house edge, savvy players can capitalize on their knowledge of the game to increase their bankroll. Additionally, participating in the casino's daily and weekly promotions can further boost earnings. While luck plays a role, mastering Blackjack can turn the tables in your favor, making it a top choice for those looking to cash in at the Diamond Casino.