Index exchange-traded funds (ETFs) are a great way to invest. Most combine diversification, low fees, and solid performance -- making them an ideal choice for investors who want to set it and forget it.

So today, I'll reveal my top choice among all index ETFs, and examine why it's likely to remain a great choice well into the future.

Which index ETF is the best?

For me, there's a clear choice when it comes to which index ETF I want to own for the long term. It's the Invesco QQQ Trust Series I ETF (NASDAQ: QQQ).

This fund is linked to the Nasdaq-100 index, which tracks 100 stocks listed on the Nasdaq exchange. Top holdings include all of the "Magnificent Seven:" Apple, Nvidia, Microsoft, Amazon, Alphabet, Meta Platforms, and Tesla.

In addition, many other prominent tech stocks like Broadcom, Netflix, and Advanced Micro Devices are included among its holdings.

What you won't find are financial stocks. By rule, the Nasdaq-100 excludes any stocks from the financial sector.

Because of its heavy allocation of tech stocks, the index, and by extension, the fund, has been the top-performing benchmark index over the last 10 years -- hands down.

For example, when comparing the fund against others that track the S&P 500, the Dow Jones Industrial Index, and the Russell 2000, the Invesco fund's superior performance shines through.

Over the last decade, the fund has generated a compound annual growth rate (CAGR) of 19%, meaning a $10,000 investment made at the start of the period would have grown to almost $57,000 today.

By contrast, the SPDR S&P 500 ETF Trust, an ETF that tracks the S&P 500 index, generated a CAGR of 13.9%. The SPDR Dow Jones Industrial Average ETF ranked third with a CAGR of 12.6%, and the iShares Russell 2000 ETF came in last with a CAGR of 9%.

What's more, those are total returns, meaning that dividend payments have been included in the annual return calculation. On a strictly price return basis, the Nasdaq-linked fund performs even better compared to other benchmark indexes.

Why this fund is likely to outperform well into the future

So, it's clear the Invesco fund has been the best choice over the last decade -- but what about the future? Why should investors still view the fund as the best choice?

The main reason why the fund is a solid investment is its focus on innovative, growth-oriented companies. Consider one of the fund's top holdings, Nvidia.

Nvidia has grown its annual revenue from $26 billion in 2022 to close to $100 billion today. Over the next two years, analysts expect the company's annual revenue to skyrocket to nearly $180 billion.