I must respectfully disagree,LOL... The stock market. There are 2 types of people that play with the stock market. Suckers, and insiders. If you're not one, you're the other.
Starting at a young age, paying for a good adviser and learning for yourself along the way is the reason so many working middle class folks can afford to live comfortably in retirement. That's been my plan since my mid 20's and it's working for me. HI's and low's for sure but nothing is guarantied in life.