Is SCB or IB cheaper if I'm going to DCA every quarterly, S$2500 every 3months into IWDA? I just turned 21yo, so I'm allowed to apply SCB, and below 25yo so monthly activity fee on IB is $3. Any advice?

One thing others here seemed to have missed - you mentioned that you are 21 and hence IBKR will only charge 3 USD minimum commission per month until you turn 26.

Assuming that you don't have Standard Chartered Priority (which gets rid of the minimum commission per trade)... you definitely will have lower total commissions on IBKR. In your case, DCA quarterly will be cheaper, though not by much.

IB all the way. SCB has minimum comm fees of $10 at 0.25% of trade. And charges horrendous FX spreads of atleast 0.8% this means you lose an additional $20 for every trade of S2.5k (if in a foreign currency). IBKR on the other hand charges close to spot rates (like google conversion).

That's on top of the terrible lack of service from SC Bank - don't even bother really. Worst mistake of my investment journey - They have incredibly inflexible custodian structures that prevents you from transferring your securities should you decide to switch brokerage.