The best index fund in my opinion is Vanguard S&P 500 ETF or VOO. The stock is expensive at 232.86 but it has fallen from a 52 week high of 311 and a 52 week low of 200. The stock is currently at 232.86 and a good buy, but as the market is crashing I believe the ETF will go in the 100s. A few of the stocks biggest positions Microsoft, Apple, and Amazon. The stock owns mostly large companies and normally grows 9.23% averagely per year.
This brings stable returns as well a dividend of 2.05%. VOO is a index fund for anyone as you put the money in when you want then forget about it and get good returns. An investment of 1000, in March 2015 would now be worth 1555 with a return of 55%. I think this index fund is great for any investor that is willing to hold it a long term.