What is the difference between saving for retirement via a insurance plan compared to placing it in a SA. Which is better?

Insurance plan offers you protection coverage such as death, disability coverage, coverage depends on the types of savings insurance plan that is purchased, as different insurance plan may come with slightly different protection coverage.

the best thing about putting into savings account is it allows more flexibility and liquidity in your money withdrawing. but savings account most of the time does not come with protection coverage. so the key maybi to put some money for your liquidity needs, and to set aside some money for your retirement savings and protection needs with a good insurance product

I think you need to think about what you are trying to do. It sounds like you want to cover both objectives of insurance and saving together.

SA cant help u for accidents and illness.
By the other side, insurance endowment plans also dont necessarily do well at returns for retirement.

Probably better to carve out different budgets for each. Having said that, it is very very difficult to beat cpf sa risk free interest rate consistently year after year.