Are you wondering if the Standard & Poor's 500 index is a good place to park your investment dollars? Warren Buffett says that the best retirement plan is to put 10% of your funds in short-term government bonds and 90% in an S&P 500-tracking exchange-traded fund (ETF). As Buffet is one of the world's foremost investors, you could do worse than to take his advice. (See also: Warren Buffett's Investing Style Reviewed.)

The S&P 500 is perhaps the best depiction of the U.S. economy, covering all the main sectors and representing roughly 80% of the nation's market cap. It's not surprising that nearly $10 trillion of investor cash is tied to the equities that make up the index—according to the latest statistics from S&P Dow Jones Indices—over $3.4 trillion of which is in index ETFs. (See also: Index Mutual Funds vs. Index ETFs.)

Of course, not all S&P 500 ETFs are created equal. Some do a much better job of replicating the benchmark, and others do so at enviably low costs compared with their competitors. You've found your investment sweet spot when you discover a fund that manages to perform well at an attractive cost. (See also: The 10 Cheapest Vanguard ETFs.)

If you're thinking of moving some cash into an S&P 500 index ETF, here's a look at some top picks for the fourth quarter of 2018. Funds were chosen on the basis of a combination of assets under management (AUM), expense ratio and long-term performance. Year-to-date performance was a factor, too, but after the recent selloff, year-to-date gains are modest, with each up around 10%. All figures were accurate as of April 9, 2019.

1. SPDR S&P 500 ETF (SPY)

  • Issuer: State Street Global Advisors
  • AUM: N/A
  • 2019 YTD Performance: N/A
  • Expense Ratio: N/A

While technically not an ETF (SPY is a unit investment trust, which are typically more tax-efficient vehicles than managed funds), this is the oldest of the S&P 500 benchmarked funds and by far the largest in terms of AUM. It is also extraordinarily cheap to hold, with an expense ratio of just 9 basis points, and it very closely tracks the performance of the benchmark index.

The fund is also extremely liquid, with an average daily trading volume of nearly 16 billion per day, which makes it attractive as a tactical trading instrument as well as a buy-and-hold investment for fleshing out a 401(k). Benchmarked returns are solid over the 1-year, 3-year and 5-year period, with gains of 17.83%, 17.21% and 13.82%, respectively. (See also: How ETFs Are Dominating the Stock Market.)

2. iShares Core S&P 500 ETF (IVV)

  • Issuer: BlackRock
  • AUM: $169.5 billion
  • 2019 YTD Performance: 16.14%
  • Expense Ratio: 0.04%

If you're looking for straight-up S&P 500 exposure at rock-bottom prices, IVV is the fund for you. It's difficult to find a fund that delivers tight benchmark performance with such low holding costs. Of course, it can't come close to SPY in terms of volume, but IVV is plenty liquid for just about every class of investor, with over 850 million shares changing hands every day. It is also a true ETF, which means it avoids the cash drag inherent in a unit investment trust like SPY. Benchmarked returns are strong over the 1-year, 3-year and 5-year period, with gains of 9.39%, 13.46% and 10.86%, respectfully. (See also: Yes, Investors Buy and Hold ETFs.)

3. Vanguard S&P 500 ETF (VOO)

  • Issuer: Vanguard
  • AUM: $459.65.82 billion
  • 2019 YTD Performance: 16.02%
  • Expense Ratio: 0.04%

With an inception date of September 2010, VOO is the newest of these three ETFs, but it's a part of Vanguard's well-respected portfolio of funds. You might be tempted to wonder if there's really much difference between VOO and its primary peers IVV and SPY, and in all honesty, there's not a lot. Like its peers, VOO has low costs and high liquidity, and it offers the large-cap coverage you expect in an S&P 500 benchmark fund.

While the differences may be minor, they are potentially important. VOO only discloses its holdings on a monthly basis—not daily like IVV—which is a slight ding in terms of transparency. And VOO, unlike SPY, reinvests its interim cash. Benchmarked returns are strong over the 1-year, 3-year and 5-year period, with gains of 9.40%, 13.46% and 10.86% respectively. (See also: A Look Inside the Vanguard S&P 500 ETF.)

Key Takeaways

  • Warren Buffett says that the best retirement plan is to put 10% of your funds in short-term government bonds and 90% in an S&P 500-tracking exchange-traded fund (ETF).
  • The S&P 500 is perhaps the best depiction of the U.S. economy, covering all the main sectors and representing roughly 80% of the nation's market cap.
  • Some S&P 500 ETFs do a much better job of replicating the benchmark, and others do so at enviably low costs compared with their competitors.

Access to the Markets

To get access to these ETFs one would need an investment account through a stock brokerage. Researching the investments that you would like in your portfolio can be a challenge, and so can choosing the broker that best fits your needs. In the pursuit of sound advice, Investopedia has put together a list of the best online brokers based on their prices and their features to help those searching for a broker along in their hunt.