Are you the sort of investor who embraces the buy-and-hold strategy, preferring to do your due diligence up front and then let the returns accumulate over time? If so, index-based exchange-traded funds (ETFs) may be a good vehicle for you. Even Warren Buffett knows it's hard to beat index funds. In fact, he made a point of requesting that 90% of the money he leaves his wife when he dies be invested in an S&P 500 index fund. 

Of course, you don't have to park all your money in an S&P 500 fund. In fact, most experts recommend some diversification. But as far as long-term investments go, indexed funds are an attractive and typically low-cost choice. Investopedia has put together a list of the best online stock brokers for stock trading if you're looking to get started with ETFs. 

If you're doing some portfolio planning for the rest of 2018, here are a few good bets for ETFs that work for long-term investors. All year-to-date (YTD) performance figures are based on the time period of Jan. 1, 2018, through September 25, 2018. Funds were selected based on a combination of performance over time and assets under management (AUM). All figures were current as of September 25, 2018.

1. The Vanguard Total Stock Market ETF (VTI)

  • Issuer: Vanguard
  • Assets under management: $107.43 billion
  • YTD performance: 10.26%
  • Expense ratio: 0.04%

If you're not sure which index to follow, or you want to hedge your bets across a variety of sectors and market caps, this is the fund for you. As the name implies, the Total Stock Market ETF covers the entire domestic stock market, tracking the CRSP U.S. Total Stock Market Index. VTI is a balanced fund, with a good mix of mid- and small-cap equities, in addition to blue chips. The median market cap is about $54 billion. You'll also see good sector diversification among the 3,462 stocks in its basket.

VTI is an extremely efficient fund with a low expense ratio. The stock is now trading at $150.53, near its all-time highs of over $146, hit on January 26, 2018. Since hitting that high, the stock has see-sawed a bit. Investors will need to decide if current levels warrant an entry or if it is better to hold off a bit longer. Long-term performance figures are steady and impressive, with one-year, three-year and five-year average annual returns of 20.28%, 15.86% and 14.25%, respectively. (For related insight, read more about whether VTI is the best index fund.)

2. The SPDR S&P 500 ETF (SPY)

  • Issuer: State Street Global Advisors
  • Assets under management: $274.95 billion
  • YTD performance: 9.71%
  • Expense ratio: 0.09%

This is the granddaddy of ETFs – the oldest and most easily recognized of the exchange-traded funds. It tops the list in terms of AUM and trading volume, making it appropriate for both tactical traders and buy-and-hold investors. The fund tracks the S&P 500, which is a group of equities from the U.S. large-cap space (although not always the largest) selected by a committee. 

Technically, SPY is a unit investment trust (UIT), which means that the fund can't reinvest cash dividends between distributions, a minor detail that may slightly affect performance compared with the index. Regardless, this fund has respectable one-year, three-year and five-year performance figures at 19.49%, 12.39% and 15.98%, respectively. 

3. The iShares Core MSCI EAFE ETF (IEFA)

  • Issuer: iShares
  • Assets under management: $58.38 billion
  • YTD performance: -1.86%
  • Expense ratio: 0.09%

IEFA delivers exposure to developed-market stocks in Europe, Australasia and the Far East, excluding domestic and Canadian equities. Its benchmark index, the MSCI EAFE, covers about 98% of investable markets and includes small caps in proportion to the market, which is something that competing funds don't do. Japan and the U.K. take the top two spots in the fund's portfolio, which is tilted toward financials and industrials.

There are 2,483 equities in the fund, which is well diversified, with the top ten holdings accounting for 9.4% of the total portfolio. This is a highly liquid fund with tight spreads and low ownership costs, making it a good choice for both long- and short-term investors who want exposure to markets outside of North America. The fund is newer than the other two, with an inception date of October 18, 2012. Year-to-date, the price of the stock has seesawed and is currently unchanged. Nonetheless, the one-year, three year and five-year performance figures are positive, at 4.65%, 7.84% and 6.45%, respectively. (For related insight, read more about IEFA's ongoing growth.)