The optimal number of decks for blackjack generally favors fewer decks. Single-deck and double-deck games offer the lowest house edges, around 0.17% and 0.38%, respectively, when using basic strategy. These are ideal for players looking to minimize the house advantage. However, casinos tend to offer fewer single-deck games, and card counters can exploit these situations more easily. As the number of decks increases, such as with 6 or 8 decks, the house edge rises slightly to around 0.5% or 0.6%, and card counting becomes less effective. Therefore, if you're aiming for the best odds, fewer decks are typically better, but the choice also depends on the game rules and whether you plan to use advanced strategies.