I did a trip similar to this and agree with you that the Singapore Flt 12 SIN-NRT-LAX legs were the best!
I think I had a premium economy window seat on the upper deck with only two across seating. Lots of storage space on the side. The A380 was fabulous and the cabin crew was extremely friendly.
Of course, just before I flew, the scandal with the wing crack issues had just hit the fan and this caused me a little concern. I could see "scars" out on the wings, so I convinced myself that this was one of the birds that had already been repaired.
Regards,
Max