Forex, also known as the foreign exchange or FX market, is the world's most traded market, with a $5.1 trillion daily turnover. In simple words, Forex trading is the process of converting one country's currency into another country's currency, aiming to profit from the changes in its value.

1. Volatility. The Forex market is highly volatile. Predicting the movements of a single currency pair, which can be influenced by numerous factors, is essential. In contrast, when trading indices, you predict the broad movements of a stock market, which is generally less volatile.
2. Liquidity. Some stock market indices are less liquid than the Forex market, the largest and most liquid market globally.
3. Time strategies. Indices trading may be more suitable for long-term traders. On the other hand, Forex trading tends to be more convenient for short-term traders who prefer to profit from small price changes.
4. Leverage. In FBS, Forex trading offers the maximum possible leverage of 1:3000, whereas indices are traded with leverage up to 1:33.

Please remember that it is better to choose trading instruments based on your trading strategy, level of knowledge, understanding of the particular market, and risk tolerance.