People treat SPY vs VOO like a rivalry. It isn't. It's the same fund wearing two price tags.
Both track the S&P 500. Same companies, same weights, same returns give or take fees. So the entire ETF vs ETF comparison comes down to one number: 0.09% for SPY, 0.03% for VOO. That's it. If you're shopping for the best S&P 500 ETF, run a best low cost S&P 500 ETF comparison and VOO wins on cost every time, because the portfolios are identical and only the fee moves.
Let me put numbers on it, because percentages lie by sounding small. On $100,000 held 30 years, that 0.06% gap compounds into thousands of dollars. For the exact same index. That's not a rounding error. That's a vacation.
So why does SPY still exist at this size? Traders. SPY is the most traded ETF on the planet, with spreads you could drive through and an options market nothing else touches. If you trade options or move serious size, SPY earns its fee. If you're buying every month and holding, you're renting liquidity you'll never use.
Now the question I keep hearing: should I own both SPY and VOO? No. That's the S&P 500 twice, with part of it costing triple. Usually it happens by accident. Bought SPY years ago, read that VOO is cheaper, bought VOO too, never cleaned up. Or two accounts with two different defaults. It's understandable. It's also fixable in one trade. In an IRA, just consolidate and move on. In a taxable account, mind the gains before you touch anything.
Tax treatment? Identical. Qualified dividends, same structure. There is genuinely nothing else to decide.
For the full picture with IVV and SPLG added, ETFCompare runs the fee math side by side. Start at etfcompare.fyi.