Which connects best to Davao?

Other than that it's down to personal preference. Some prefer the chance to break the journey hence 25/26 work well for them, If looking for award availability you may even end up being stuck with SIN-FRA-JFK on SQ326/SQ26, which means an overnight in FRA, and actually not bad at all and or/ SQ25->SQ325 which is an afternoon in FRA, which is probably not so good. Some prefer to depart in the evening and arrive first thing in the morning (SQ23 and SQ22). I prefer departing in the morning and arriving in late afternoon/early evening (so I don't need to stay up for a whole day on arrival) (SQ21 and SQ24).

The other of course if you have a preference for EWR or JFK.

In summary, if you don't have a preference for EWR or JFK, focus on the timings you might prefer, in flight really not that much of a difference.