The best investment method i think is trading. But you must know about market price before you try it. You can hold your BTC for several weeks or months than you look market price. The other way is altcoin trading. It's faster than BTC trading, but it has high risk, so i don't recommend it. The last thing i want you to know, be careful when you choose trading site or you'll lose your BTC 
i want to add that with great risk comes great rewards. especially now that bitcoin market is stable and boring, altcoin market is a good choice for getting some good profit out of it.of course it is not easy and not for everyone to jump in and start profiting, it is a good way to double or triple your investment in a short time.