the fastest option is the early morning flight on AA from jfk to lhr connecting with QR to KTM (via doh) - on the way back you can follow a similar routing. QR participates in Star Alliance so you may have to combine two awards. Another good option is the austrian air seasonal flight (only on fridays) with a stop in vienna. EK to DXB - connecting to GF in Auh is another good one as DXB and AUH are only about 1.5 hours from each other by taxi and you could make a stopover in DXB - but GF has few options for awards - as does the EK flight. The Direct flight to Sin - connecting to royal Nepal may be another option - RN it is not a bad airline safetywise, but with a lot of delays. I would avoid Delhi - it's better to fly in via Bkk or Kul if you want to avoid a long layover in Del. If you make a stopover in Delhi it is a good option as it is a pretty interesting place.
Rather a long email but one last thoguht - Nepal is and has been prefectly safe for tourists - the only problems are general strikes which close down the capital for days at a time - and you may be in the wrong place at the wrong time - e.g. during a violent demonstration. All in all, it depends on your travel experience and your comfort level. I go regularly and still enjoy the place and feel very safe - despite the problems.