After-Tax Advantages Savings Account, most flexible tax-advantaged account type.
Roth IRAs are like Traditional IRAs, except that they allow you to withdrawal any contributions you’ve made at any time without penalty. These accounts are the most flexible for that reason. You also don’t ever run into a “force distributions” age. Note you still have to be 59 1/2 to withdrawal both your contributions and the growth.
529 Accounts have a similar behavior, but are for education - not retirement.