When exploring the best slots to use free play, look for games with high return-to-player (RTP) percentages and engaging features. Popular choices include "Starburst," known for its vibrant graphics and expanding wilds, and "Gonzo's Quest," which offers exciting avalanche mechanics. Additionally, classic favorites like "Book of Dead" provide thrilling bonus rounds. Always check for slots with low volatility for a better chance of frequent wins, maximizing your free play experience. Remember, the goal is to enjoy the gameplay while potentially boosting your bankroll!