In my opinion as a trader of crypto, forex and stock. The best and safe among three is Crypto.

You can't earn a good money in Forex without high leverage. But if you have a mistake, your position will get liquidated. In my opinion Forex is the fastest way to earn from your investment granting you will not make any mistake.

In stockmarket, it would take 3-5years for your investment to double.

In crypto, there are hundreds of coins to choose from. Some coins are pumping 3x to 5x a month. Just choose a good coin with high marketcap.