Nobody wants to hear this, but VOO vs VTI is a debate about almost nothing. And I mean that as good news.
VOO is the S&P 500: about 500 of the biggest US companies. VTI is the whole US market, something like 4,000 names. Sounds different. Then you look at the weights. The giants dominate both funds, so the portfolios end up looking like cousins who dress alike. The question people actually type into Google is how much do VOO and VTI overlap, and the honest answer is a lot. Most of VOO's weight sits inside VTI. You can confirm that in seconds with an ETF overlap analyzer app, iOS and Android both, which is a nice use for a phone: checking redundancy while you're inside your brokerage app.
So which is the best ETF for your portfolio? Depends what you want in one sentence. VOO if you want the cleanest large-cap benchmark and nothing else. VTI if you want the small and mid caps tagging along for free. Same 0.03% fee either way. Same manager. Same result, basically. This is a preference, not a decision. Anyone insisting one destroys the other is selling you a newsletter.
Here's the actual mistake: owning both. I've seen portfolios holding VOO and VTI side by side, which is just paying for one fund and getting the illusion of two. Pick one. Spend the saved brainpower on your savings rate, which matters roughly a hundred times more.
And if you already own one? Don't switch. The tax bill and the hassle dwarf the difference. This debate is for new money, not old money.
When you're ready to compare ETFs side by side, ETFCompare puts expense ratios, overlap, and returns for 108 ETFs on one screen. Start at etfcompare.fyi.