RA is also 4% right?
so whats the difference to have it in SA or RA? or even to move from SA to RA?
Yes, the interest rate is the same. RA is set aside for your CPF LIFE payouts, and of course that's perfectly fine. Remaining, and any additional, SA funds can be withdrawn from age 55. (They shouldn't be withdrawn, though, unless and until you actually need them. On demand funds earning 4% are absolutely lovely.)
also, which is actually a more "value for money? FRS or ERS? the payout does not seem to be linear/proportionate. infact BRS has the highest payout ratio?
All CPF LIFE levels are great values in lifetime annuities, the very best value Singapore dollar lifetime retirement annuities available. They're so good that they rival the best Wall Street has to offer, and Wall Street isn't really offering the same thing.
The only question, really, is how much longevity insurance you want. None of the CPF LIFE payout levels are lavish, so I'd just opt for ERS-level CPF LIFE (and for my spouse/partner too), and most likely pick the Escalating Plan and start payouts from age 70. For relatively well-to-do and higher people, that's the smartest and best play available. I certainly wouldn't downgrade from FRS-level with a property pledge, even if I could.
One exception: if you already have excellent or better longevity insurance (guaranteed lifetime annuities). As it happens, I/we do. So my decision is more complicated, but at the moment I'm aiming for FRS-level CPF LIFE across the household (still Escalating Plan, age 70).
To net it out, in my view you make CPF LIFE the best it can possibly be as longevity insurance, and that's FRS-level (or preferably above if CPF LIFE is your only longevity insurance), Escalating Plan, age 70. If you can afford it, of course, and most people in this forum can (or will).
Then...and here's the truly magical part...go have FUN, lots of it, knowing that you've got a guaranteed stream of lifetime retirement income that'll take you all the way to the end, even if that's age 108. Money is only useful to exchange for goods and services, at some point in time. That's the only thing it can do. So nail down the long tail well and best, and then have fun.