The iShares S&P 500 ETF (ASX: IVV) and the Betashares Nasdaq 100 ETF (ASX: NDQ) are two popular ways for ASX investors to access US shares.
I think both are strong long-term investments.
But the better choice comes down largely to how much concentration and volatility an investor is comfortable accepting.

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Why I like the IVV ETF
The IVV ETF tracks the S&P 500 Index, giving investors exposure to around 500 of America's largest companies.
I like it as a core holding because the portfolio reaches across technology, healthcare, financial services, industrials, consumer businesses, and other major parts of the US economy.
There is still plenty of exposure to companies benefiting from technological change. Nvidia, Microsoft, and Amazon are among the major businesses represented.
But the investment case does not depend as heavily on technology remaining the strongest part of the market.
That makes the IVV ETF the option I would favour if I wanted broad US exposure and something I could comfortably keep adding to through a wide range of market conditions.
Why take more risk with the NDQ ETF?
The NDQ ETF tracks the Nasdaq 100 Index, which contains 100 of the largest non-financial companies listed on the Nasdaq.
Its portfolio is much more concentrated in technology and growth businesses. That could work particularly well if areas such as artificial intelligence, cloud computing, semiconductors, digital advertising, and software continue expanding strongly over the next decade.
I also like that the Nasdaq 100 can change as new corporate leaders emerge. Investors are not locking themselves into today's biggest technology companies forever.
The trade-off is that the NDQ ETF can be much more sensitive when growth shares fall out of favour.
A sharp sell-off in technology can hit a large portion of the portfolio at once, while the IVV ETF has more exposure to other industries that may behave differently.
For investors comfortable riding through those swings, I think the extra concentration could also provide greater upside if its major growth businesses continue performing strongly.
Which would I buy?
If I wanted the more balanced option, I would choose the IVV ETF.
It still gives me access to many of America's leading growth companies, but I would be spreading my money across a much wider section of the economy.
If I had a higher tolerance for risk and wanted greater exposure to technology-led growth, I would lean towards the NDQ ETF.
There is also no reason investors necessarily need to choose only one. Holding both would increase exposure to many companies that appear in each index, so I would just be conscious of that overlap.
Foolish takeaway
For me, this is less about identifying a winner and more about choosing the ETF that suits the investor.
The IVV ETF would be my preference for someone wanting broad US exposure with less concentration.
The NDQ ETF could suit investors willing to accept more volatility in pursuit of stronger growth.
I think both can be excellent buy and hold investments when matched with the right risk tolerance.