What each one does
Both strategies pay the minimum on everything and put every spare pound or dollar against one target debt. The avalanche method targets the highest interest rate first. The snowball method targets the smallest balance first.
Avalanche is mathematically optimal: it always costs less interest and is never slower. That is not in dispute.
Why snowball still wins for some people
Clearing a small debt entirely produces a visible result in weeks rather than years, and one fewer account to manage. For anyone who has abandoned a payoff plan before, that early finish line is doing real work.
The question worth asking is not which is optimal but what the difference actually costs you. Run both against your real balances and rates. If avalanche saves a few hundred over five years and snowball is the one you will stick to, snowball is the better plan. If the gap is thousands, that changes the answer.
What to check before either
Two things outrank both strategies. First, whether a balance transfer or consolidation at a materially lower rate is available to you, which can save more than any ordering ever will. Second, whether you have enough cash set aside to handle a surprise, because the usual way a payoff plan dies is an unexpected bill going back onto the card you just cleared.