Does anyone have any thoughts as to which JFK-HKG nonstop flight is more comfortable. Does anybody have any thoughts? Also, any preferences for seats?

There will be two of us flying in J on 30 January:

CX841
JFK 09:15
HKG 14:25+1

or

CX831
JFK 13:55
HKG 19:05+1

Thanks. I tried to do some searches on this, but was unable to find anything.