They're both tax advantaged accounts - meaning you don't have to pay taxes on them in most situations.

HSA is supposed to be a Health Savings Account, but has turned into more of a retirement account. 401k is Americas sad replacement for pensions as workers need to contribute to it and so it largely only helps wealthier people.

The more general advice would be - make sure to save and invest money (preferably in ways that avoid taxes if possible).