Indices and stocks are not the same thing. An index is a statistical measure of the change in a portfolio of stocks. It is not itself a stock, but rather a composite of the performance of a group of stocks. Stocks, on the other hand, are individual securities that represent ownership in a particular company.

There is no one "best" index for trading. The best index to trade depends on your investment goals, risk tolerance, and other personal factors. Some popular indices for trading include the S&P 500, NASDAQ Composite, and Dow Jones Industrial Average.

It is difficult to rank indices, as different indices are designed to track different types of market segments and have different methodologies. Some of the most well-known indices include: S&P 500, NASDAQ Composite, Dow Jones Industrial Average, FTSE 100, Nikkei 225.

It is possible to trade on FOREX and to trade indices, but they are quite different markets. FOREX is about trading currencies, while indices represent the performance of a group of stocks. It is not possible to say whether one is "better" than the other, as the choice of which market to trade will depend on the individual trader's goals and risk tolerance.