HKG, SIN, KUL, and PEK all have direct flights to DAC (on KA, SQ, MH or AK, and MU, respectively).

Assuming that you're a US citizen, keep in mind that you'd need a visa for PEK (unless just transiting, which seems to not be what you're planning).

In my personal order of preference for logistical reasons assuming an NYC departure: HKG, PEK, SIN, KUL.

SIN is an annoyingly long jaunt from NYC; HKG and PEK are more reasonable (though it's harder to make a case for PEK if you don't already have a visa). KUL-DAC is going to be hard or impossible to do on the same ticket as the rest of your trip, so I'd say this is the worst form a logistical/convenience perspective.

If, as it appears from your list of possible stopover candidates, you're looking for the typical southeast Asia experience, KUL is probably your best bet. There's a ton of fun stuff to do in KUL and Malaysia. If you've never been to PEK, I'd definitely recommend it as well. HKG and SIN, of course, are just your standard Asian megacities.