It depends on your goal. If you want the best bet, AND you know how to play PERFECT Basic Strategy in Blackjack, then that is your game.
If, however, you just want to relax, have fun, and make your money last a long time, then you might consider Roulette. Bet the minimum bet on "Red" or "Black", get some free drinks, chat it up with people, and cheer when folks win. If you do this, your money could last a long time.
Blackjack moves much quicker than roulette. You may lose less percent of your money in the long run per bet, but if the game moves fast enough, you still can lose more actually money just because of the sheer number of bets you're playing.
Slot machines are easily the worst.