The avalanche method always wins mathematically. The snowball method wins for many people psychologically. Here's the honest comparison.
Avalanche: pay minimums on all debts, put every extra dollar toward the highest-interest-rate debt first. When that's paid off, roll that payment to the next highest rate. Snowball: pay minimums on all debts, put every extra dollar toward the smallest balance first. When that's paid off, roll to the next smallest.
Avalanche always saves more total interest because it eliminates high-rate debt faster. The difference can be hundreds to thousands of dollars depending on your debt balances and rates. The calculator shows the exact difference for your specific debts.
Research suggests people who start with the smallest balance are more likely to stay on track and pay off all their debt. The early wins from eliminating entire debts quickly provide motivation that the avalanche method — which can feel slow when your highest-rate debt is also large — sometimes doesn't. If you've struggled to stick to debt payoff before, the extra interest cost of the snowball method may be worth the higher completion rate.