To be honest, JAL economy seats are the best in the industry. Service wise - I think JAL F/As might be a bit more reserved especially for non-Japanese speakers, but in general, both airlines have great F/As with great attitude. Catering wise - I prefer JAL because my own personal taste, and JAL also offers a second light refreshment service (packaged pastry) on SIN flights. SQ offers only one full hot meal on Japan flights. Entertainment wise - JAL is just bad. WiFi - both airlines are similar.

Honestly I will fly JAL economy (international) because of legroom and wider seats especially on 787s.

Both airlines are fairly good so you will not go wrong with your decision.

Carfield