Forex is bigger than bitcoin trading because Forex has been here for a longer time than Bitcoin and Forex has many currency that you can trade including Bitcoin. The similarities is they both are speculative market that you have to speculate where the market is going to move next. Bitcoin is younger than forex and it should have more advantages therefore if you are looking for which one to learn or start trading, I will choose Bitcoin. Bitcoin has more opportunities because you can just accumulate Bitcoin instead of trading it and if you buy Bitcoin for trading and you did not interpret the market well then you miss selling for profit, you can abandon trading and start accumulating Bitcoin and when the price of Bitcoin reaches a new highest price, you are going to make very big profits. Forex trading is regulated but Bitcoin trading is not regulated which causes more volatility but it provides you with opportunity as well to profit.