If you're paying an M-class fare level, then buying a lower UA fare and using the extra cast to upgrade to E+ might give you a bit more comfort, but you'd have to transit via a US gateway. However, if you need the flexibility to change the return it's a toss up. (Do you really need that flexibility at another $1,000?) Another comfortable alternative likely to be found at a similar fare to AC's M, is EWR-SIN-HKG on SQ's nonstop to SIN (though you'd likely hav to sind the cheapest fare through an ethnic TA). The economy seats offer somewhat more pitch than their other flights. TG would also offer slightly enhanced economy seating of its version of this to BKK from JFK. However, your flexibility requirement may not make these alternatives of use.