yet people are complaining that it has been a bad investment
I think that is because in the long run, people tends to be used in the fast changing price of Bitcoin and that is not dumping but they are used to pumping. Since the price are changing fast, they always think that it will always be a pump and they are scared of the dump. They are complaining since they are scared of what may happen in their investment.
Getting scared in the crypto market because of the changes in the prices of the investment is actually ridiculous. This is the mistake which most of the newbies in the market make and suffer losses out of their panic selling. The market study clearly shows that price fluctuations are very normal and tend to affect the market. So there is a need of some patience for your investment to bear some positive and good returns for you. If you lack that patience, then you can never become a successful trader in the market.
And as far as the best investment is concerned, bitcoin hits up the mind always. But there are also many other profitable alternatives also that can be bought at cheap rates and fetch you good market returns. Diversification of the portfolio is always a good option and the best investment strategy one can opt for!