Depends on your spending type actually,Simple answer... Lazy.
For context, before Covid, I focused on Miles cards, Citi Premier Miles.
Their miles do not expire and have the widest range of exchange partners
My logic then was that no matter how high the cash rebates are, redeemed air tickets are usually worth even more. I was also accumulating miles to treat family to aspirational travel trips which I would not have spent cash on.
When Covid hit, I decided to stop the miles accumulation and switched to cash rebates. But I do not want to track spend category, maximum value, minimum spent etc. My first cashback card then was Standard Chartered Unlimited cashback, pretty simple and easy to use but there are categories that was exempted.
Then this March, I read about how to leverage on Amex + Grabpay and the rest was history. When I first signed up for the Amex in March, the welcome offer was huge. $270 ($250 + $20) CapitaVouchers plus the 3% for 1st $5,000 spent. Plus Amex have no limitations and when combined with the GrapBay, it seems like the best balance between "most" rewards for "least" effort.
unless your spending is mostly insurance, education, tax payments, and other generally excluded spending,
A general rebate card like UOB one (5% $2000 monthly spend) will be useful and give u more rebates than (AMEX+GPMC)
U shd keep GPMC as a card for specialized use (gov, LTA, tax) since there is a cap of $30,000 per year.