Question: Is the DOW index fund a good investment or is the S&P 500 a better investment?

Depends on the business cycle. At certain points in the business cycle, major industrials do well, at other points, medium sized companies do well, at other times small cap companies do well. Understanding the business cycle will help you determine which would be the better investment at this point. In phase two (right now) large industrials do best because of their excess capacity.

Answer:

The DJIA has increased in value more consistently than the NASDAQ or S&P 500 index