At the moment, I am still using my SCB Amex Card simply because of the still-hard-to-beat 6x bonus points when you use it for overseas transactions and selected travel agents in HKG. I bought many tickets from that particular TA with the SCB Amex card because of that benefit; for example: I just authorized around $13k of tickets from HKG, which is equivalent to slightly more than 5k miles for that single transaction. Not to mention that at the moment (till end of the month), SCB Amex still has that Double Miles Promotion for local transactions, which is equivalent to 4x bonus points and the redemption rate is still at $12=1AM; free of charge.
As for other transactions in which Amex is not accepted, then, I will still use the Citibank Premier Miles; except for Dining transactions, which will go to the DBS Master Card, because of the 3x bonus points. Occasionally, when the DBS Black Card has some value-for-money promotions (like at the end of last year), I will also use it once-in-a-while.
These 4 are my most frequently used cards nowadays.