Several Vanguard ETFs are good candidates to buy. The Vanguard S&P 500 ETF (NYSEMKT: VOO) is a perennially smart pick for long-term investors. Probably the only major knock against this fund is that it's historically expensive right now with a price-to-earnings (P/E) ratio of 27.5.

While the stock market doesn't offer any guarantees, top-rated ETFs have a higher chance of delivering on their promises. Whether you want to beat the market or generate high cash flow without much volatility, an ETF with a five-star rating from Morningstar is more likely to get the job done.

Simpler is better in the long run, particularly if you're only looking to deploy a fairly small amount of money.