Best Way To Track The S&P: SPX or SPY?

Hi there,

I was reading a book here on fundamental analysis, the author recommends using the SPY to track the stock market and makes no mention of the emini futures.

Is there any reason for that? Trying to look into it couldn't find anything.

Thanks

This one:

https://www.amazon.com/Profiting-For.../dp/0071464654