In Puzzle 5, you should play JAW to block your opponent’s setup. JAW is better than TAW because the J is a fairly large liability in thus position, Playing the J will allow you to score minimally well while only turning over a few tiles and giving yourself a smaller chance to draw a vowel.
Failing to block isn’t an option, as there are too many devastating plays that your opponent can draw in this position. Your opponent is also under no obligation to use the setup next turn: if he doesn’t draw something that scores well, he can play elsewhere and preserve that setup for later. Because of this, you should block the setup and sacrifice equity now, taking out the setup threat both next turn and into the future.