The S&P 500 (SNPINDEX: ^GSPC) is arguably the stock market's most important index. It tracks the 500 largest U.S. companies on the market, and it has become the benchmark for U.S. and international investors.

The oldest exchange-traded fund listed in the U.S. has just been surpassed in assets under management by a Vanguard ETF that more cheaply tracks the S&P 500 index.

With Vanguard taking the top place among the ETF providers, it is now time to consider two of its ETFs with over 10% upside potential in the next 12 months. These include Vanguard Communication Services ETF (VOX) and Vanguard Dividend Appreciation ETF (VIG).

The Vanguard S&P 500 ETF has an exceptionally low expense ratio. Having your money in an S&P 500 ETF instantly diversifies your portfolio. Slow and steady is a great way to earn money over time. Here are a few reasons why putting $100 into the Vanguard S&P 500 ETF right now and holding it for the long term is a wise decision.