I think NH's regional C service isn't all that (from my experience), but their longhaul C is likely considerably better (from what I've read). Their staggered business looks pretty decent.

If you're flying on a US *A award (which I assume you are given the mileage price and the username, though you didn't mention it), you should be able to route through another region without additional charges as long as you aren't taking a stopover (and sometimes even if you are). The problem is that I don't think you can get a C award on SQ's EWR-SIN flight (it's blocked to *A), and JFK-FRA-SIN-(wherever it is you're going in China) is the REALLY long way around (plus the factor that depending on where you're going, you might be connecting in PVG or PEK to CA domestic), though as long as SQ is flying 747s, it's theoretically open to *A awards (I saw some decent advance availability some time back).

Since you don't care about lie-flat and want decent IFE/food/service, as long as you don't care about all the extra flying, sure, you could fly SQ out of JFK- though reports are the 747 IFE and seats are getting flakey towards the end of their time in the SQ fleet (if this is far enough in the future, you also might luck out into A388 C if they equipment swap on you). I sat in a 772ER Spacebed seat and it was fine for what it was- it's not the latest and greatest but it's acceptable, and the food and booze on SQ regional C was better IMO than TG regional C, NH regional C... or UA longhaul F.

You also didn't mention CA or CO on your list. Did you consider them and find them unacceptable?