I'm 24 years old. Should I top up my CPF SA or buy AVIVA my retirement plan? Which one has better outcome?

They are different plans actually. A closer fit to CPF SA would be Aviva MylifeIncome.

But since you're so young, why not start investing instead? Monies topped up into CPF are irreversible and provides 0 liquidity until you're 55.

You can definitely stomach some risk and try to achieve closer to double digit returns for the next 15 to 20 years before you hit your mid 40s which would then be a time where you look for more guarantees and less risk.