The best ETF comparison tool is the one you open before you buy, not after you regret. Could be a website. Could be the best ETF screener app on your phone. The checklist doesn't change either way.
Five minutes, five checks. One: expense ratio. The only fee you pay with certainty, every year, win or lose. Two: what it actually holds, because two funds with similar names can own very different stocks. Three: overlap with your existing portfolio, which is where most people quietly fail. Four: tracking difference, meaning how closely it follows the index after costs. Five: tax treatment, which matters more for bond and international funds.
The fee math is worth sitting with for a second. A 0.5% fee versus a 0.05% fee over 30 years can cost you tens of thousands on a six-figure portfolio. Fees compound against you with the same math that returns compound for you. Same engine, opposite direction.
My unpopular opinion: the comparison that actually matters is fund versus doing nothing. A mediocre cheap index fund that gets funded every month beats a perfectly optimized portfolio that never gets its first deposit. Analysis good. Paralysis expensive.
Also check the fund's age and size. Tiny brand-new ETFs close sometimes, and a closure is a forced taxable event plus a scramble. A fund with real assets and a few years of history is simply a safer parking spot.
After the purchase, the job isn't over. A mobile portfolio tracker app with alerts keeps you honest about drift, which is the part everyone skips. And if you want training wheels on the allocation itself, an ETF portfolio builder that makes you choose the mix before the funds will teach you more than any ranking ever could. Any decent ETF screener should cover all of the above.
ETFCompare runs fees, overlap, and returns for 108 ETFs on one screen. Start at etfcompare.fyi.